refactor: remove support for disk configuration source

What does this MR do?

This can be merged only in 14.3 and it needs to wait for #571 (closed).
It would be good to merge !495 (merged) before this so that more code can be nuked.
There are a couple of issues about performance/availability issues with disk source, I assume they can be closed since they won't be relevant once this is merged: #68 (closed) and #158 (closed)

Closes #382 (closed)
Closes #68 (closed)
Closes #158 (closed)
Closes #103 (closed)
Closes !478 (closed)
Closes !230 (closed)
Closes !237 (closed)

Blocked by #571 (closed)

TODO

• I added the Changelog trailer (e.g. Changelog: feature) to the commits that need to be included in the changelog
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines