Maven POM downloader optimizations

[ammachado]

What's changed?

This PR introduces two small optimizations to MavenPomDownloader:

1. Add a trailing '/' to Maven repository URL checks to avoid HTTP 302 redirects on slow Artifactory instances. Also tag the repository URL as known, if able to connect to it.
2. When deriving metadata for artifacts present on the local maven repository, consider only successfully downloaded artifacts.

This PR also fixes the counting of deriveMetadata successful calls.

What's your motivation?

Increased latency when working on network restricted environments with slow Artifactory proxies.

Anything in particular you'd like reviewers to focus on?

No.

Anyone you would like to review specifically?

Have you considered any alternatives or workarounds?

No workarounds for environment issues

Any additional context

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files

[timtebeek]

Thanks a lot @ammachado !