Non-existant group index 200s not 404s

In NEXUS-23487 there was an expectation that a non-existant (remote) index file would 404. This was not implemented as part of that effort and instead it continues to 200 as it did before the regression. However, the team believes this may still be errant and this ticket is to address it.
This only happens for group and not for proxy.

Example: http://localhost:8081/repository/pypi-group/simple/noneexistsright/

Note, from a UI perspective, the page loads with the header of the index however it has no contents (see attached). Nothing saves to DB/blobstore.