feat: allow granular selection of GitHub notification method via destination

[tonglil]

trafficstars

Right now if someone has all of the GH notification types configured, subscribing to it will update all of them without a way to choose which one.

This is useful when you want to use commit status for one type of trigger, and deployments for another.

The change retains the existing behavior: if no recipient is specified in the subscription annotation, all notification types will be updated.

[tonglil]

Ping @pasha-codefresh or any other owner?

[pasha-codefresh]

Will review. Sorry for delay

[tonglil]

Darn, drifted too much