feat: document wundergraph/cosmo#1758

Author: seancribbs

docs/router/configuration.mdx

@@ -1361,9 +1361,10 @@ We support NATS and Kafka as event bus provider.
           url: "nats://localhost:4222"
           authentication:
             token: "token" # or
-            user_info:
+            user_info: # or
               username: "username"
               password: "password"
+            credentials_file: "/path/to/user.creds"
       kafka:
         - id: my-kafka
           tls:
@@ -1394,6 +1395,7 @@ We support NATS and Kafka as event bus provider.
 |  |authentication.user\_info| <Icon icon="square" /> |User-Info based authentication. | |
 |  |authentication.user\_info.username| <Icon icon="square" /> |Username. | |
 |  |authentication.user\_info.password| <Icon icon="square" /> |Password. | |
+|  |authentication.credentials_file   | <Icon icon="square" /> |Path to an JWT/NKey credentials file. | |
 
 ### Kafka Provider