feat: add login type 'none' to prevent password login (#8009)

* feat: add login type 'none' to prevent login

Users with this login type must use tokens to authenticate.
Tokens must come from some other source, not a /login with password
authentication

coderd/database/migrations/000126_login_type_none.down.sql

@@ -0,0 +1,2 @@
+-- It's not possible to drop enum values from enum types, so the UP has "IF NOT
+-- EXISTS".

coderd/database/migrations/000126_login_type_none.up.sql

@@ -0,0 +1,3 @@
+ALTER TYPE login_type ADD VALUE IF NOT EXISTS 'none';
+
+COMMENT ON TYPE login_type IS 'Specifies the method of authentication. "none" is a special case in which no authentication method is allowed.';