Add Dangerfile for Internal Users changes

What does this MR do and why?

• Adds a Dangerfile for changed files that change internal users
• It appends to the top-level comment with a warning to implement documentation (optionally, as it could be wrong)
• Adds comment per line

The regexes combine the internal bot names found in users/internal.rb and check for their usage, or changes around their def and end, or their usage in other code like :internal_bot

References

• Issue #480172

How to set up and validate locally

1. Checkout the branch 480172/add-danger-for-internal-users-change
2. Make a change to internal.rb or files with any bot usage (git add + commit)
3. Run bin/rake danger_local