Suggest existing organisations / teams on signup with matching non-generic domains

[kyle-ssg]

Is your feature request related to a problem? Please describe.

A common problem is that users incorrectly create a duplicate organisation because they haven't received / seen an invite from their team.

Describe the solution you'd like.

• Allow users with non-generic emails to see existing organisations created by users with the same domain.
• Allow users to request an invite to an organisation

Additional context

This was brought up as a way to improve time to first feature / improve onboarding