Draft: [RECORD_DEPRECATIONS] Simplify setup of DeprecationToolkit

What does this MR do and why?

This MR simplifies the setup of DeprecationToolkit by using the builtin methods of recording deprecations.

Initial recording of deprecations

1. Record deprecations (when MR title contains RECORD_DEPRECATIONS for now)
2. Download deprecations/ and commit them into the repository
3. New and removed deprecations will fail locally and on CI.

Day to day use

1. Change code and run specs which fail deprecations where adedd or removed
2. Adjust deprecations/ accordingly or run re-record deprecations for specs in particular
3. Commit deprecations/

This way it's very clear and visible which deprecations to fix and which were resolved. Similar to RuboCop's TODO list.

Screenshots or screen recordings

n/a

How to set up and validate locally

n/a

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.