Change Sidekiq testing mode to `fake` instead of `inline`

What does this MR do?

This changes the Sidekiq mode from inline to fake in the test environment.

This should hopefully make RSpec jobs run faster.

Documentation has been updated:

Sidekiq jobs are typically not run in specs, but this behaviour can be altered in each spec through the use of perform_enqueued_jobs blocks. Any spec that causes Sidekiq jobs to be pushed to Redis should use the :sidekiq_inline trait, to ensure that they are removed once the spec completes.

The :sidekiq_might_not_need_inline trait was added when Sidekiq inline mode was changed to fake mode to all the examples that needed Sidekiq to actually process jobs. Examples with this trait should be either fixed to not rely on Sidekiq processing jobs, or their :sidekiq_might_not_need_inline trait should be updated to :sidekiq_inline if the processing of background jobs is needed/expected.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/16098.

changed milestone to %12.3

added Quality bugperformance ci-build test labels

changed the description

	3 Warnings
	This merge request is quite big (more than 939 lines changed), please consider splitting it into multiple merge requests.
	a59d10e3: This commit’s subject line is acceptable, but please try to reduce it to 50 characters.
	1cfc54a2: This commit’s subject line is acceptable, but please try to reduce it to 50 characters.

Reviewer roulette

Changes that require review have been detected! A merge request is normally reviewed by both a reviewer and a maintainer in its primary category (e.g. frontend or backend), and by a maintainer in all other categories.

To spread load more evenly across eligible reviewers, Danger has randomly picked a candidate for each review slot. Feel free to override this selection if you think someone else would be better-suited, or the chosen person is unavailable.

Once you've decided who will review this merge request, mention them as you normally would! Danger does not (yet?) automatically notify them for you.

Category	Reviewer	Maintainer
backend	Tetiana Chupryna (@brytannia)	Sean McGivern (@smcgivern)
test for spec/features/*	No reviewer available	No maintainer available
frontend	Scott Hampton (@shampton)	Filipa Lacerda (@filipa)

Generated by Danger

added 94 commits

• 821a4971...2369e488 - 91 commits from branch master
• fe22073a - Make 'Sidekiq::Testing.fake!' mode as default
• a23244de - Introduce new :sidekiq_inline{,_tech_debt} RSpec tags
• 8a753852 - Add the :sidekiq_inline_tech_debt to specs that needs Sidekiq

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added Enterprise Edition label

added 507 commits

• 8a753852...5e97743f - 504 commits from branch master
• 6e36d2e9 - Make 'Sidekiq::Testing.fake!' mode as default
• e1c7865b - Introduce new :sidekiq_inline{,_tech_debt} RSpec tags
• 3c9ce493 - Add the :sidekiq_inline_tech_debt to specs that needs Sidekiq

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added 28 commits

• 3c9ce493...aaed3f5e - 25 commits from branch master
• 2097d9bd - Make 'Sidekiq::Testing.fake!' mode as default
• 7701424f - Introduce new :sidekiq_inline{,_tech_debt} RSpec tags
• f52943fd - Add the :sidekiq_inline_tech_debt to specs that needs Sidekiq

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added 1 commit

• 2beabf69 - Fix a nil error in Gitlab::Danger::Teammate

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added 127 commits

• 2beabf69...6160611b - 124 commits from branch master
• 69c01b66 - Make 'Sidekiq::Testing.fake!' mode as default
• d133f6f8 - Introduce new :sidekiq_inline{,_tech_debt} RSpec tags
• 60de6ac3 - Add the :sidekiq_inline_tech_debt to specs that needs Sidekiq

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added 1034 commits

• 60de6ac3...b920d5b1 - 1031 commits from branch master
• 2456ea99 - Make 'Sidekiq::Testing.fake!' mode as default
• 9df68d7b - Introduce new :sidekiq_inline{,_tech_debt} RSpec tags
• ae939de0 - Add the :sidekiq_inline_tech_debt to specs that needs Sidekiq

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added 44 commits

• ae939de0...34980e3d - 41 commits from branch master
• 7f1158c1 - Make 'Sidekiq::Testing.fake!' mode as default
• 7ac24e93 - Introduce new :sidekiq_inline{,_tech_debt} RSpec tags
• 33845387 - Add the :sidekiq_inline_tech_debt to specs that needs Sidekiq

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marked the checklist item Documentation created/updated or follow-up review issue created as completed

added 104 commits

• 33845387...5b304f01 - 101 commits from branch master
• 89271615 - Make 'Sidekiq::Testing.fake!' mode as default
• 96595c2a - Introduce new :sidekiq_inline{,_tech_debt} RSpec tags
• 1f757ba3 - Add the :sidekiq_inline_tech_debt to specs that needs Sidekiq

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added 14 commits

• 1f757ba3...4d0875c0 - 11 commits from branch master
• 26e3fe9e - Make 'Sidekiq::Testing.fake!' mode as default
• ff9018cc - Introduce new :sidekiq_inline{,_tech_debt} RSpec tags
• d45fb118 - Add the :sidekiq_inline_tech_debt to specs that needs Sidekiq

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added 14 commits

• d45fb118...c499724b - 10 commits from branch master
• 48fc6c8f - Make 'Sidekiq::Testing.fake!' mode as default
• 8ada9ab1 - Introduce new :sidekiq_inline{,_tech_debt} RSpec tags
• 7e723402 - Add the :sidekiq_inline_tech_debt to specs that needs Sidekiq
• f66efe59 - Document the new :sidekiq_inline trait

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added backstage [DEPRECATED] label

assigned to @vzagorodny and unassigned @rymai

added 382 commits

• f66efe59...3eb9dcb4 - 378 commits from branch master
• 0e5bdff2 - Make 'Sidekiq::Testing.fake!' mode as default
• 49087dfd - Introduce new :sidekiq_inline{,_tech_debt} RSpec tags
• 105ad8d1 - Add the :sidekiq_inline_tech_debt to specs that needs Sidekiq
• 81e6e4c4 - Document the new :sidekiq_inline trait

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