Add note about --server-issued-login to the docs

The current situation is that our Identity Provider auth.spacetimedb.com it's having a domain name issue, so when SpacetimeDB tries to validate that this is a valid token issued by auth.spacetimedb.com, it fails to validate. This would be as if you had selected "Sign in With Google" and Google's auth server was down.

SpacetimeDB itself, both your local version, and Maincloud, have no dependencies on that auth service directly, but your token specifies that its issuer is auth.spacetimedb.com because it's your developer account which you can use both locally and in Maincloud. This allows you to have the same identity across multiple clusters and to recover your account if you lose your token or see your Maincloud databases on the website.

You can, via --server-issued-login use SpacetimeDB as a local Identity Provider, but be advised it is not a fully featured Identity Provider. So if you lose the SpacetimeDB issued token you have lost access to that identity and you're a bit SOL, so for that reason we recommend using your auth.spacetimedb.com developer account even when you connect locally.

We should probably add this into some of the docs