Deprecate events and hooks in 8.x-7.x

Problem/Motivation

Codebase on 8.0.x is changed. We need to deprecate some/all of the hooks and events.

Steps to reproduce

Proposed resolution

Remaining tasks

- Make summary of all events and hooks that needs to be deprecated
- Create change record with code samples how changes should be done
- Add deprecations to 8.x-7.x codebase.

User interface changes

API changes

Data model changes