Add a new ruby3 branch synchronization pipeline schedule

What does this MR do and why?

Add a new ruby3 branch synchronization pipeline schedule.

• A new project token is created and called ruby3-sync: https://gitlab.com/project_278964_bot10
  • It has read_registry and write_repository permission as a developer
  • It will expire in 2023-10-01 (I expect we remove this before it's expired)
• A new CI/CD variable is created and called RUBY3_SYNC_TOKEN
  • It's protected and masked
    • After merged: Re-enable protected because it's disabled for testing in this merge request
  • The scope is set to ruby3-sync
  • The value is the project token for ruby3-sync
• A new branch ruby3-sync from an orphan commit is protected, and maintainers can merge, no one can push
• A new branch ruby3 from master is protected, and maintainers can merge, ruby3-sync can push
• A new pipeline schedule "Sync ruby3 branch every odd hour"
  • After merged: Enable the schedule https://gitlab.com/gitlab-org/gitlab/-/pipeline_schedules

Examples:

• Sync: https://gitlab.com/gitlab-org/gitlab/-/jobs/2967995146
• A pipeline is triggered: 8399d974

Setting screenshots

Project token ruby3-sync

(Note: The screenshot was outdated, and it should have permission for read_registry and write_repository instead)

CI/CD variable RUBY3_SYNC_TOKEN

Protected branches ruby3-sync and ruby3

Pipeline schedule

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

See #340298 (comment 1041169793)