Simplify elasticsearch maintenance callbacks

What does this MR do?

ApplicationVersionedSearch installs three callbacks - create, update, and destroy - on including models.

This MR moves the relevant code into methods so it can be modified or overridden more easily. Upcoming changes are going to complicate the update logic, including per-class special casing, so this should make it easier to handle.

!24298 (merged) introduces an alternative processing mechanism for these events, which is another complicating factor. Holding it in a callback proc will (ahahaha) hold us back.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Part of #34086 (closed)