feat(maven): Unify fetching utilities

[zharinov]

Changes

Replace checkResource and checkS3Resource with updated downloadMaven function which supports everything we need: timestamps, private registry detection and, well, the content itself

Context

Documentation (please check one with an [x])

• I have updated the documentation, or
• No documentation update is required

How I've tested my work (please select one)

I have verified these changes via:

• Code inspection only, or
• Newly added/modified unit tests, or
• No unit tests but ran on a real repository, or
• Both unit tests + ran on a real repository

[viceice]

can we split this into smaller parts? it's pretty hard to understand all changes.

and I also think this is a feature because you drop the head requests. that doesn't look like a refactor to me. it's at least a fix.

refactor PRs are not causing releases, so they accumulate

[zharinov]

can we split this into smaller parts?

I don't think so, since it would contain duplicate code and will require duplicate tests.