BundlerChecksum: Add command to lint gems checksums

What does this MR do and why?

BundlerChecksum: Add command to lint gems checksums

This command checks if every gem has a corresponding checksum stored. It does not verify the checksum though.

To avoid failing CI pipelines let lefthook lint gems when Gemfile.lock has changed and ensure that every gem has a checksum stored.

Contributes to #414374 (closed).

Screenshots or screen recordings

No gem changes ✅	Gemfile.lock changed without checksum 💥	Gemfile.lock with checksum changes ✅

How to set up and validate locally

1. Add gem "foo" to Gemfile (see httos;//rubygems.org/gems/foo)
2. Run bundle install
3. Commit the changes git commit -m 'Add gems' Gemfile*
4. Run bundle exec lefthook run pre-push 💥
5. Run bundle exec bundler-checksum init
6. Amend the latest commit git commit --amend -m 'Add gems' Gemfile*
7. Run bundle exec lefthook run pre-push ✅

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.