Persist refspecs when create a pipeline

What does this MR do?

Currently, the system compose refspecs when runner fetches the job. This implementation leaves a significant race condition that refspecs could vary per the external dependencies state, such as merge request's WIP flag.

The system has to persist the refspecs when it creates a pipeline instead of composing refspecs dynamically.

What are the relevant issue numbers?

Related https://gitlab.com/gitlab-org/gitlab-ee/issues/7380

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer