Migrate extensions from URIs to URNs

[benbellick]

See substrait-io/substrait#856 for context.

This will require temporarily handling both URIs and URNs, and then later dropping URI support.

This change depends on first bumping the version of substrait once a new substrait release occurs.

[nielspardon]

@benbellick were you planning to also cover the changes for Python? I'm asking since we would benefit from having substrait-python updated to use the URNs now that substrait-java has been updated. If it's not on your list I could ask someone from my team to help out here. Let me know.

[benbellick]

Hi @nielspardon. I actually had just started working on it yesterday. Will open up a PR when the change is ready.

[nielspardon]

Hi @nielspardon. I actually had just started working on it yesterday. Will open up a PR when the change is ready.

awesome. looking forward to it