SSO with multiple domains

## Important Details

How are you running Sentry?

[ x] On-Premise docker [Version 10.0.0.dev0]

## Description

I want to configure Google Auth with multiple domains whitelisted. At the moment only the default domain is allowed to configure, but I need a second one (not sure where it gets the first one though, configured external dns?)

## Steps to Reproduce

1. configure `sentry/sentry.conf.py`

```
SENTRY_OPTIONS['auth-google.client-id'] = 'ID'
SENTRY_OPTIONS['auth-google.client-secret'] = 'SECRET'
SENTRY_OPTIONS['auth-google.domains'] = [ 'domain1.org', 'domain2.org']
```
2. rebuild & rerun
```
docker-compose build
docker-compose run --rm web upgrade
docker-compose up -d
```

### What you expected to happen

I expected to be able to login with SSO from both domains.

Is that the right approach?

Many thanks,
bert