Allow multiple users to register with an organization

New flow:

• If there are no users on the instance, I am shown the register page (because of checking hasUsers on the health endpoint)
• After that I’m shown the login page (how it works now)
• However, you can manually navigate to /register without being redirected
• You can create a new user with an organization

after this it should still not be possible for a user to be in two organizations since users are only associated with orgs when the user is created (via invite code or via registering)

Introduce a new environment variable:

ALLOW_MULTIPLE_ORGS=true

which defaults to false

When creating an org, we should check if there is an existing org and whether multiple orgs are allowed.

Registering as a new user

Replace registerInitialUser with registerNewUserWithOrg

Currently used on POST /register - this should not be restricted to only a single user. Many people can register to use Lightdash.

All users that register this way will get their own organization

https://github.com/lightdash/lightdash/blob/7745f86b414c9e07aa83de53d5ae7fd5f1c4d3a0/packages/backend/src/services/UserService.ts#L450-L450

[PriPatel]

Yeah bin it!

[ZeRego]

That works if we don’t mind people filling up a form to get an error.

We also need to:

• delete every use of needsSetup returned by the health endpoint. Which currently controls when the register page is available and when to redirect to the register page.
• delete/update the welcome page. I don’t think this page makes sense anymore. 🤔 @PriPatel