Allow registering SNAPSHOT versions into the registry

[vsevel]

Today when we register a LTS released version and a SNAPSHOT, we only see the SNAPSHOT version in code-quarkus-app.
@gastaldi has already pushed #264
But it does not seem sufficient according to this zulip comment.
We are very interested in the possibility of registering SNAPSHOT versions in relation to our release cycle:
we a version of the Quarkus platform gets released (e.g. 3.16), we move our extensions to 3.16, and keep them in SNAPSHOT on the main branch.
we let people test and integrate this new version. We push fixes to our extensions during that period. At the end of this period, we bump to the latest version of Quarkus, for instance 3.16.3, and we create a release of our extensions. For instance 3.6.0 (pointing to Quarkus 3.16.3).
Without support for SNAPSHOT we have to release an ALPHA version, and applications created on this version would stay on that released version, and they would not get the fixes that come naturally from the SNAPSHOT version.
So what we would like when we move our extensions to 3.16, is registering immediately our 3.6.0-SNAPSHOT into the registry. and when we released 3.6.0 , then we replace the SNAPSHOT version into the registry by the release.
That way we do not have to release an ALPHA version just to please the registry.

[vsevel]

the rule for SNAPSHOT seems to be: "to no longer show in the registry is when a final release related to that SNAPSHOT is available"