chore: Lowercase OCI reference before pushing

[joonas]

Motivated by bytecodealliance/wasm-pkg-tools#134.

This uses bash parameter expansion with the ,, operator to lowercase the entire input.

[yoshuawuyts]

thank you for filing this! I'm wondering though: is this the right place to fix this? Shouldn't we fix this in wkg instead?

[joonas]

I don't know if it's appropriate to roll this into wkg itself due to the fact that it might be getting used against non-conformant registries (i.e. ones that do allow for uppercase letters), and it might be surprising to have wkg lowercase the name automatically for you there (though maybe it should be behind a flag? not sure).

I suppose the same could be said for this action, but it seemed like a more appropriate place to have this logic since the likelihood of this being used against ghcr.io or other OCI conformant registries is much higher, and having those pushes fail due to uppercase letters is rather unfortunate.