feat(deploy): Support for Preview Channels

[lacolaco]

Firebase Hosting finally supports the Preview Channel feature!

https://firebase.googleblog.com/2020/10/preview-channels-firebase-hosting.html

So I think ng deploy should allow developers to choose the channels.

# Just a proposal inspired by https://github.com/marketplace/actions/deploy-to-firebase-hosting

{
  "builder": "@angular/fire:deploy",
  "options": {
    "channelId": "preview",
    "expires": "7d"
  } 
}

[jamesdaniels]

Absolutely aiming to support this. Need to bump the firebase-tools version in the next release.

[abdel-ships-it]

Any idea when this is ready? The documentation in here is somewhat out of sync with the out of the box setup of ng add @angular/fire

[Drofzz]

any update on this?