In PRs, add some pre-merge checklist depending on changed files

[pajlada]

When we update src/messages/Message.hpp and add a new element, we need to make sure it also updates toJson if applicable and the clone function.

Can we somehow automatically add a label or something if that file is modified in a PR to hint: "HEY YOU NEED TO CHECK THIS" to the reviewer?

PRs where this has been missed:
#7192

[Mm2PL]

I think we could make the clang-tidy action send a comment.

[pajlada]

Would clang-tidy be able to check if any change has been made to e.g. MessageElement.hpp or MessageElement.cpp and send a notice?