Separate openapi-extractor versions by external repo

[provokateurin]

Currently we use a single version of openapi-extractor which works just fine right now.
Unfortunately this will no longer work in the future if we want to get the latest improvements of openapi-extractor.
Some apps are lacking behind quite a bit and I doubt they will get fixed any time soon.
This will fragment the versions of openapi-extractor and might make fixing some bugs in it harder as each upstream repo has to bump first, but it has been quite stable in recent months and it removes the burden of manually updating openapi-extractor to the latest "working" (lowest common denominator between all repos).

In principle we can do this already, but unfortunately drop_account doesn't have openapi-extractor as a dev dependency. I already pinged the maintainer so we will hopefully have that.
One last thing to consider is the version of openapi-extractor that will be used for merging the specs, but I think it's pretty safe to go with the one from server as I also maintain it there. The merge script hasn't changed for a while already, so it's likely not going to cause many problems in the future either.

[provokateurin]

https://framagit.org/framasoft/nextcloud/drop_account/-/issues/27

[provokateurin]

For example notifications will required v1.2.1, but apps like tables can not use it yet. So we have to definitely do this to move forward.