Steps to reproduce:

1. Use Symfony in debug mode.
2. Add plenty of "Folder" contents - it can be 1000 or more.
3. Update "Folder" Content Type and add any field to it.
4. Save.
5. Can be repeated for deleting a fieldtype as well.
6. Observe the performance of POST request, both in terms of time and Doctrine queries.

Result:
Depending on number of contents a request can timeout or just take a really long time. Amount of queries run is ~3 x number of contents, some installations have millions of contents which results in the functions being unusable.

Expected result:
Implement proper scaling for this functionality.

Note:
The issue comes from ContentUpdater\Action\AddField and ContentUpdater\Action\RemoveField being used for every content.