Draft: Add lefthook config

What does this MR do?

This MR adds an initial Lefthook config for gitlab.

It adds a couple of backend hooks:

• pre-commit:
  • rubocop on staged files
• pre-push:
  • rubocop on files changed against the main branch
  • bin/rake gitlab:sidekiq:all_queues_yml:check

Additionally, it adds lefthook run lint with bin/rake gettext:lint. The idea is to add long-running tasks under this section, it would be unpractical to run those in pre-push hooks.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team