Extract discussion actions into separate component

What does this MR do?

This is a part of the work to split NoteableDiscussion component into smaller components: https://gitlab.com/gitlab-org/gitlab-ce/issues/55566

Discussion actions have been moved out of NoteableDiscussion into a new DiscussionActions component:

The goal is to have a better separation of concerns in this part of the app, which should result in easier to maintain components and fewer regressions in the future.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Closes #58293 (closed)