Add client_id to Application Context

What does this MR do?

This MR adds the client_id to the context. It's value is one of the following, in order of precedence:

• user/user.id
• runner/runner.id
• ip/request.ip

Tasks:

• Add client_id into labkit-ruby (https://gitlab.com/gitlab-org/labkit-ruby/-/merge_requests/60)
• Modify Gitlab::ApplicationContext to add client_id
• Remove all direct access to Labkit::Context (done here: !56003 (merged))

In addition, it removes wrapping every spec in a separate context, thereby avoiding unnecessary context initializations. Wrapping can still be enabled by using the context_aware flag.

Issue: gitlab-com/gl-infra/scalability#126 (closed) and #321831 (closed)

Does this MR meet the acceptance criteria?

Conformity

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Availability 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
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
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