fix: Add username idx (#11918)

* Add index on 'users.username'

* Bring back fields that are in main

packages/prisma/migrations/20231016125421_add_username_idx/migration.sql

@@ -0,0 +1,2 @@
+-- CreateIndex
+CREATE INDEX "users_username_idx" ON "users"("username");

packages/prisma/schema.prisma

@@ -253,6 +253,7 @@ model User {
   @@unique([email])
   @@unique([email, username])
   @@unique([username, organizationId])
+  @@index([username])
   @@index([emailVerified])
   @@index([identityProvider])
   @@index([identityProviderId])