Update timeout/timeout_source getter/setter methods and apply feature flags

What does this MR do and why?

Context

Since some job metadata will be moved to new destinations (e.g. intrinsic data moved to ci_builds and immutable processing data to ci_job_definitions) we need to be able to use feature flags to read/write data to specific destinations.

timeout and timeout_source are intrinsic data that will be persisted in p_ci_builds.

This MR

Updates the timeout/timeout_source getter/setter, moves them to Ci::Metadatable and applies the following feature flags:

• read_from_new_ci_destinations (Roll out: #552063 (closed))
• stop_writing_builds_metadata (Roll out: #552065 (closed))

Also fixes the affected RSpec tests.

NOTE:

• The timeout_value method was introduced in !196948 (merged). This MR applies the other timeout-related changes based on the POC !193948 (diffs).
• The BuildMetadata API entity and presenter will be updated as part of #552059 (closed), which will use the new methods introduced in this MR.

UPDATE: The new job update_timeout_state is gated behind a feature flag:

• FF: ci_use_new_job_update_timeout_state
• Roll-out issue: #566611 (closed)

References

• Resolves part of #552057 (closed)
• Related to Fix presenters and API entities exposing CI bui... (#552059 - closed)
• Roll out issue for new feature flag: [FF] `ci_use_new_job_update_timeout_state` -- W... (#566611 - closed)

How to validate

This tests that the feature works before and after enabling the feature flags.

1. First with all feature flags disabled:

Feature.disable(:read_from_new_ci_destinations)
Feature.disable(:stop_writing_builds_metadata)
Feature.disable(:ci_use_new_job_update_timeout_state)

2. Update the pipeline configuration with the following:

job:
  script: echo

job-with-job-timeout:
  script: echo
  timeout: 1m 25s

3. Run the pipeline and view each job's details. Observe that they have their timeout and time source correctly populated.

4. Enable ci_use_new_job_update_timeout_state and repeat steps 2 & 3.

5. Enable read_from_new_ci_destinations and repeat steps 2 & 3.

6. Enable stop_writing_builds_metadata and repeat steps 2 & 3.

• This won't work yet because we need to update the build metadata entity/presenter in #552059 (closed).

MR acceptance checklist

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Related to #552057 (closed)