fix(mok): Add KILL capability

This patch hopefully fixes issues with sending kill signals to subprocesses from the master process of dovecot.

Exmaple error logs:
```
Jan 25 00:27:16 master: Error: service(auth): kill(14, SIGINT) failed: Operation not permitted
Jan 25 00:28:16 master: Error: service(auth): Process 14 is ignoring idle SIGINT
```

charts/mok/values.yaml

@@ -152,6 +152,8 @@ dovecot:
         - SETGID
         # -- required to create spool directories
         - FOWNER
+        # -- required by management process to keep subprocesses in check
+        - KILL
       drop:
         # -- required to drop privileges by default
         - ALL