gftools packager: refactor

[m4rc1e]

Following PR refactors the packager to meet the following criteria:

• Drop upstream.yaml files since metadata files now have all the necessary source fields
• Simplify the commands based on feedback received from users
• Aggressively simplify. Users weren't too fussed by interactive mode so this has been dropped
• Add a batch packager so we can update all families in the collection
• Simplify code. Codebase is now a quarter of the size and far easier to understand
• Add onboarder checklist to pull request messages
• Don't onboard families that lack family categorisation tags.

[simoncozens]

Somehow this rewrote my repository_url to https://wwwhub.com/.......

[simoncozens]

Hahaha!

    metadata.source.repository_url = metadata.source.repository_url.replace(".git", "")

[m4rc1e]

@simoncozens I'm very happy with your new commits. Happy to merge if you're happy?

[simoncozens]

Yes, LGTM.