Support filling in an extension's publisher

[sqs]

It would be nice if src extensions publish could fill in the publisher with the access token's username. This would make it easier for users who want to publish a "fork" or local dev copy of an extension. It would mean they would not need to temporarily edit package.json to add a "publisher": "jsmith" property (and remember to avoid committing their changes).

[felixfbecker]

I would be afraid to accidently republish extensions from a personal account that are published by an org

[eseliger]

Extensions have been deprected, so I am going to close this ticket as part of some backlog grooming. Please reopen if you think we should still care about it.