Introduce sign-up restrictions

[gtsiolis]

Problem to solve

Given that the role of self-hosted in our strategy becomes more relevant over time, more feature requests and needs will show up in the long run. See relevant RFC (internal).

One of these needs is the ability to provide more fine grained control over sign ups. See relevant discussion.

Proposal

TBD (To be discussed)

The following scenarios could be helpful:

1. Disable new sign ups
2. Require approval for new sign ups
3. Require user email confirmation
4. Allow sign ups only for specific email domains

[corneliusludmann]

The only mitigation we have currently in place is to block new users (optionally with a passlist):

gitpod/chart/values.yaml

Lines 281 to 283 in baa41ec

	blockNewUsers:
	enabled: false
	passlist: []

gitpod/.werft/values.dev.yaml

Lines 45 to 48 in baa41ec

	blockNewUsers:
	enabled: true
	passlist:
	- "gitpod.io"

gitpod/installer/example-config.yaml

Lines 3 to 5 in baa41ec

	blockNewUsers:
	enabled: false
	passlist: []

[mrsimonemms]

An additional consideration could be to allow sign ups from specific organisations. I'm not sure how this would work with BitBucket (and any future oauth-providers we support), but it should be possible with GitHub and GitLab.

For the record, the blockNewUsers is supported natively by the Installer as well and the configuration is identical to @corneliusludmann's example above:

gitpod/installer/example-config.yaml

Lines 3 to 5 in 72f109c

	blockNewUsers:
	enabled: false
	passlist: []