Enqueue worker that Publish SLSA provenance statement when job ends with artifacts

Why are we doing this work

As a part of Phase 2: Generate provenance statement in control plane , we need to enqueue a job to publish a SLSA provenance statement when a job ends with artiacts.

The worker that publishes the SLSA provenance of a given CI/CD job is implemented in #546178 (closed).

Depending on the configuration of the CI/CD job, this might happen when the job fails. See artifacts:when keyword.

This is a behavior change and is behind the feature flag.

Relevant links

Non-functional requirements

• Documentation: Merge #426764 (closed) as part of this work.
• Feature flag: This is a behavior change, and it's behind a feature flag for project actor.
  • Name of the flag: slsa_provenance_statement
  • Update rollout issue with that name: [FF] `slsa_provenance_statement` -- Roll out fe... (#547866)
• Performance: see here for performance analysis https://gitlab.com/gitlab-org/gitlab/-/issues/556202
• Testing: See verification steps below.

Implementation plan

• Define and introduce feature flag.
• In the BuildFinishedWorker - add a new line to invoke "publish provenance statement worker" based on the Feature flag check
• Add unit tests

Verification steps

To be verified manually on production in a test project where the feature flag is enabled.