Schema registry does not create versions correctly after deletion

[nicolaferraro]

Version & Environment

Redpanda version: (use rpk version): 24.1.2

What went wrong?

After deleting some subject versions and recreating them, the registry shows an inconsistent state.

What should have happened instead?

I'd expect a deleted schema that is later added not to be ignored.

How to reproduce the issue?

To replicate:

curl -H "Content-Type: application/json" -X POST -d '{"schema": "{\"type\": \"int\"}"}' -i http://localhost:8072/subjects/test/versions
curl -H "Content-Type: application/json" -X PUT -d '{"compatibility": "NONE"}' -i http://localhost:8072/config/test
curl -H "Content-Type: application/json" -X POST -d '{"schema": "{\"type\": \"string\"}"}' -i http://localhost:8072/subjects/test/versions
curl -H "Content-Type: application/json" -i http://localhost:8072/subjects/test/versions
# this ^ correctly returns [1,2]
curl -H "Content-Type: application/json" -X DELETE -i http://localhost:8072/subjects/test/versions/1
curl -H "Content-Type: application/json" -X DELETE -i http://localhost:8072/subjects/test/versions/2
curl -H "Content-Type: application/json" -X POST -d '{"schema": "{\"type\": \"int\"}"}' -i http://localhost:8072/subjects/test/versions
# this ^ is accepted with {"id": 1}, as before
curl -H "Content-Type: application/json" -i http://localhost:8072/subjects/test/versions
# this ^ returns [3]
curl -H "Content-Type: application/json" -X POST -d '{"schema": "{\"type\": \"string\"}"}' -i http://localhost:8072/subjects/test/versions
# this ^ is accepted with {"id": 2}, as before
curl -H "Content-Type: application/json" -i http://localhost:8072/subjects/test/versions
# this ^ still returns [3], I'd expect it to be [3,4] but the "string" version was ignored

JIRA Link: CORE-3008