Try to prevent duplicate tenant creation

[travjenkins]

Please propose features in the Discussions area as an idea
We have users that register with Estuary after their company already has a tenant. Would like to try to get these users to not make a new tenant.

Notes:

match the email's domain to a tenant somehow

We'll need to figure out how we want to parse domains to make this usable. Not all emails are foo@example.org so we'll want to make sure we parse out usable portions.

? better prefilling or registering domains to tenants ?

If we want this it would be best if we could have a user say "register my email domain to the tenant" so that we can look these up specifically. Or we could try to autofill tenant in with the email domain.

? possibly filter out specific domains like gmail, yahoo, aol ?

If we add either of these we probably want to skip fetching/prefilling/registering with common email providers.