Sort packages by version instead of relying on ChartVersions[0]

[antgamdia]

Description of the change

As described in #6584, we were returning wrong versions in some corner cases (mainly using pre-releases). It seems we were relying on ChartVersions[0] with the explicit assumption that it would always contain the latest version. However, this is not the case. Since the DB does not know about semver (unless we used some extensions), the ORDER BY query might be wrong.

This PR is replacing the occurrences of ChartVersions[0] in favor of a previous semver sorting. The affected operations are: GetAvailablePackageDetail, GetAvailablePackageSummaries, GetInstalledPackageSummaries and GetInstalledPackageDetail.

Benefits

The latestVersion returned by the API (and therefore used by the UI -as is-, we don't sort them in client-side) will be the one that has to be.

Possible drawbacks

1. In this PR I have just tacked the Helm plugin, not the Flux one.
2. In the code we have relied on this assumption, not 100% of the side effects, if any.

Applicable issues

• fixes Google Artifact Registry-based helm chart is not defaulting to latest version #6584

Additional information

Example of a new version being properly detected:

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[antgamdia]

I have noticed (c.f. #6249) some scenarios where the versions are not semver. In those cases, I have just fallen back to the previous behavior. However, I wonder if we should replace the sorting just with a lexicographic order, instead of blindly relying on ChartVersions[0]. See what you think.

[absoludity]

Great, thanks Antonio. I was thinking the the issue may be related to the way chartmuseum was creating the index, when app versions aren't present, but realised it's GAR (OCI) so not relevant. Either way, this is much better than our previous reliance on the ordering in an index (or even in the sync code that we have for OCI repos).