Release primary key backfill migrations

We have shipped backfilling migrations to .com. This issue is about releasing those migrations, so that also self-hosted installations execute those migrations.

Tasks

• %13.12 Enable execute_batched_migrations_on_schedule feature flag by default (!61316 (merged))
• %13.12 Enable optimize_batched_migrations feature flag by default (!61317 (merged))
• %14.0 Start backfilling PK conversion for these tables (!61321 (merged)):
  • events
  • push_event_payloads
  • ci_job_artifacts
  • ci_sources_pipelines
  • ci_build_needs
  • ci_builds
  • ci_builds_runner_session
  • ci_build_trace_chunks