Add login page docs hint (#20619)

* add config field

* add endpoint

* set config var when onboarding

* add no auth exception to nginx config

* form changes and i18n

* clean up

web/public/locales/en/components/auth.json

@@ -3,6 +3,7 @@
     "user": "Username",
     "password": "Password",
     "login": "Login",
+    "firstTimeLogin": "Trying to log in for the first time? Credentials are printed in the Frigate logs.",
     "errors": {
       "usernameRequired": "Username is required",
       "passwordRequired": "Password is required",