Refactor cmd/metadata.go for clarity

[iwahbe]

Description

This PR is best reviewed commit by commit:

• 243e0a7 moves repoSlug parsing into {owner}/{name} into it's own type.
• 1bd3c23 makes mainSpec a file local variable.
• 0c8d46c moves schema fetching into it's own set of functions.
• 4b50e40 rewrites the boolean logic for determining what is a component vs a native provider vs neither.
• fbaae16 simplifies the publisher logic into a switch statement.

☝️ are pure refactors, and will not change behavior.

• 9e6554f changes the GH repo slug to require input in the form a/b where both a and b are non-empty. Previously / would have been accepted.

[t0yv0]

Would it be possible to put the codebase under test before touching it? I do not see any test files at all around this small codebase. It does not look like a lot is happening here so perhaps the testing itself does not need to be particularly complicated.

[github-actions]

Your site preview for commit 9e6554f is ready! 🎉

http://registry--origin-pr-5908-9e6554fc.s3-website.us-west-2.amazonaws.com/registry.

[iwahbe]

Would it be possible to put the codebase under test before touching it? I do not see any test files at all around this small codebase. It does not look like a lot is happening here so perhaps the testing itself does not need to be particularly complicated.

Yes. I have rebased on top of f99cca5, which adds tests for this functionality.

[github-actions]

Your site preview for commit 3963bac is ready! 🎉

http://registry--origin-pr-5908-3963bac1.s3-website.us-west-2.amazonaws.com/registry.

[github-actions]

Your site preview for commit 4e20103 is ready! 🎉

http://registry--origin-pr-5908-4e20103e.s3-website.us-west-2.amazonaws.com/registry.