Allow per channel component updates

[bbondy]

This is not for Crypto Wallets anymore since it'll be deprecated, but it would have been useful in the past for Crypto Wallets to be able to deploy some features only to our Nightly and Beta users first. E.g. the 1559 update that caused some problems for legacy users. It would have been best to discover those on Nightly and Beta.

This task is to add the ability to specify a command line parameter which would publish an extension only for a certain channel.

Internal testing that we do on the staging server is still a first step. But after that as we mature, it would be best to have extra process to deploy things that might break first to Nightly and Beta for some timeframe.