Add rake to generate jh/Gemfile.checksum.jh

What does this MR do and why?

Related issue: #2932 (closed)

• (GitLab repo) When adding a new Gem to JH, run rake bundle exec rake bundle_checksum:jh
• (Code Sync repo) Merge Gemfile.checksum and jh/Gemfile.checksum.jh to jh/Gemfile.checksum

Screenshots or screen recordings

Non UI

How to set up and validate locally

bundle exec rake bundle_checksum:jh

MR acceptance checklist

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