Configurable SSH log levels

Allow ssh log_level to be set to debug connection issues.

README.md

@@ -240,6 +240,15 @@ ssh:
   proxy_command: aws ssm start-session --target %h --document-name AWS-StartSSHSession --parameters 'portNumber=%p' --region=us-east-1 ## ssh via aws ssm
 ```
 
+### Configuring the SSH log level
+
+```yaml
+ssh:
+  log_level: debug
+```
+
+Valid levels are `debug`, `info`, `warn`, `error` and `fatal` (default).
+
 ### Using env variables
 
 You can inject env variables into the app containers using `env`: