WIP: PoC for resolving job dependencies in sidekiq

What does this MR do?

Right now we are resolving dependencies on the fly, when a new job requests comes from the runner.

We want to change the cross pipeline dependencies to:

• allow downloads for parent-child pipelines
• allow variables names in the project/job/ref fields
• increase the number of allowed cross dependencies

Before starting doing any of that I want to propose moving the execution outside of the request cycle, into the sidekiq workers just to make sure that we are not causing any availability problems. We have a preparing status for the builds, between scheduled and pending that we can use for doing the expensive computations needed to resolve dependencies.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

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

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