Description

Eventually, we'd like to move to using the "main" channel instead of the "master" channel, to be sensitive to the connotations that "master" has.

To that end, we should move the existing master-api.flutter.dev site to be main-api.flutter.dev, and create a permanent redirect from master-api.flutter.dev to main-api.flutter.dev. As an alternative, we could just create a main-api.flutter.dev redirect and point it to the existing site, but the problem with that is that it continues to propagate the "master" name in new URLs that are used to link to the site, since after redirect it ends up on the master site, not the main site.

I'm not sure exactly what is involved in this reconfiguration, but I assume it has something to do with the Firebase configuration. One complication will be to make sure that the API docs continue to be published to the renamed Firebase project, and to maintain whatever website version history we want to preserve (not much, I think, maybe the last 5 versions).

cc @godofredoc