Allow users to configure Google domain in SaaS Sentry

### Problem Statement

As for now, when the organisation owner configures SSO using Google only users under the same domain as the owner are able to authenticate and login into Sentry.

If the organisation has or wants to have multiple domains, they need to contact support as detailed in here: [https://docs.sentry.io/product/accounts/sso/#google-business-app]().

The downside of the current setup is that the customer needs to wait for the support team to reach the request, and during this period users are unable to authenticate with Sentry. The agent taking the ticket still needs to confirm: if the request is coming from an owner, if the domain is provided, if there are any issues after the change, and so on.

Not demanding tasks, but it still takes time and is something that should be possible from the user side.

### Solution Brainstorm

Allow users to add/remove domains via Organisation Settings -> Auth page.