Add time-based cleanup for Maven snapshot versions

[dianaStr7]

Pull Request: Implement Cleanup Function for Maven Snapshot Versions

Overview

This pull request introduces a cleanup function for Maven snapshot versions in Gitea, enabling more efficient management of package storage. The new feature allows users to specify how many of the most recent Maven snapshot builds to retain, optimizing storage by automatically removing older files.

Features

• New Configurable Variable: RETAIN_MAVEN_SNAPSHOT_BUILDS allows setting the number of Maven snapshot builds to keep.
  • Default is -1, which keeps all builds.
• Automated Cleanup: Tied to the cleanup expired data process, this function targets files within Maven snapshots, not the versions themselves, ensuring that only essential files are kept.

Implementation

The feature extends the existing cleanup job to include files from Maven snapshot versions based on the specified retention policy set in app.ini. It checks against the highest build number from the Maven metadata file to determine which files to retain.

Impact

This enhancement helps manage disk space more effectively by providing control over how many builds of Maven snapshots are retained, potentially reducing storage requirements for projects using Maven within Gitea.

[dianaStr7]

Considered Alternative Approach

I considered another way to handle Maven snapshot cleanup that uses the properties field for package files to store build numbers right when files are uploaded. This would make database searches simpler.

This method would need a database migration to work, so it's a bit more complicated. I have the code ready for this alternative if we think it's worth the extra steps later on.

[delvh]

Note to any reviewer: Review this PR carefully.
It seems like an LLM at the very least helped with creating this PR.
That in and of itself is nothing bad, as long as the output is indeed correct.
Given my experience with ChatGPT, I find it rather likely that it missed some edge cases though.