remove unused auth from oss-params, add deprecation notice to docs

It's optional, so no existing config should break

gso/oss-params-example.json

@@ -48,7 +48,6 @@
   "PROVISIONING_PROXY": {
     "scheme": "https",
     "api_base": "localhost:44444",
-    "auth": "Bearer <token>",
     "api_version": 1123
   }
 }

gso/settings.py

 """:term:`GSO` settings.
 
-Ensuring that the required parameters are set correctly.
+Ensuring that the required parameters are set correctly. An example file ``oss-params-example.json`` is present in the
+:term:`GSO` package itself.
 """
 
 import ipaddress
@@ -83,7 +84,9 @@ class ProvisioningProxyParams(BaseSettings):
 
     scheme: str
     api_base: str
-    auth: str  # FIXME: unfinished
+    #:  .. deprecated:: 0.1
+    #:     Not used anymore, may be left out from config file.
+    auth: str | None
     api_version: int