Move Product Intelligence Danger bot logic into a class/helper

We have now a lot of logic in the Dangerfile for Product Intelligence, we could refactor and move it in a class so we can also have tests for it.

https://gitlab.com/gitlab-org/gitlab/-/blob/master/danger/product_intelligence/Dangerfile

Maybe we could make it a plugin as changelog.rb https://gitlab.com/gitlab-org/gitlab/-/tree/master/danger/plugins