Return all graphql errors to client

Author: MetRonnie

cylc/flow/network/server.py

@@ -417,9 +417,9 @@ def graphql(
         )
         if executed.errors:
             for error in executed.errors:
-                LOG.warning(error)
+                LOG.error(f"GraphQL: {error}")
             if not executed.data:
-                raise Exception(executed.errors[0])
+                raise Exception(*executed.errors)
         return executed.data
 
     # UIServer Data Commands