Update ci_pending_builds when trackable attributes are mutated

Ref: #335866 (closed)

What does this MR do?

This MR updates Ci::PendingBuild when shared runners is toggled at the project & group level.

It includes the following items:

• Introduce new module TrackableAttribute
• Add new service to bulk update ci_pending_builds table at the project and group level
• Listen to database changes for the following attributes and kicks off service to update ci_pending_builds
  1. shared_runners_enabled for group
  2. shared_runners_enabled for project
  3. pending_delete for project
  4. builds_access_level for project

Why are we doing this?

When working on denormalization shared runners data to ci_pending_builds in !64644 (merged), it was brought up that we need to make sure to update our new denormalized column to ensure data consistency.

This MR takes care of it and add this new feature behind a feature flag ci_pending_builds_maintain_shared_runners_data.

Note: Alternatively we could use postgresql triggers as discovered in this MR

Does this MR meet the acceptance criteria?

Conformity

• [-] I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• [-] I have added/updated documentation, or it's not needed. (Is documentation required?)
• [-] I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.