Provider Registry: ability to use other build tools than goreleaser

[peterdeme]

Currently our create-version command has a strong dependency on goreleaser. We parse the artifacts.json file and go from there.

It may be a good feature to not strongly depend on it. What if someone doesn't want to use goreleaser?

As an implementation detail, this could be a good way to separate it:

# Goreleaser:
spacectl provider create-version --goreleaser-dir ./dist

# Another tool:
spacectl provider create-version --dir ./dist

Would be a minor (?) refactor in create_version.go.