Add warning when BOT_USER_TYPES changes in an MR

What does this MR do and why?

This is the second MR to close https://gitlab.com/gitlab-org/gitlab/-/issues/353645

2. GitLab generated bots should be excluded from billable members by default, i.e any similar bots created in the future, should default to not billable unless explicitly specified that they should be billable

The discussion here has more details on choosing the solution (Confidential)

Also having a warning about fixing an index as suggested here-> !106281 (comment 1203095743)

How to set up and validate locally

• Checkout the branch generated-bots-addition-warrning
• Add any new bot to the BOT_USER_TYPES in app/models/concerns/has_user_type.rb
• Run the bundle exec lefthook run pre-push (install if you don't have it)
• You should be able to get the warning

Screenshots:

Local warning:

MR warning:

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.