salt: Increase Salt master sock_pool_size and worker_threads

Time to time salt-master get overloaded because he receive to much
query, for example during upgrade and one environment a bit slow some
salt states may timeout and make the upgrade fail.
To avoid that kind of issue just bump the `sock_pool_size` on salt
master (from 1 to 15) to avoid blocking waiting for zeromq communications
and also bump the `worker_threads` on salt master (from 5 to 10) to
avoid some failure if you have too many communication with the salt
master (e.g.: because of upgrade + storage operator)

Sees: saltstack/salt#53147
(cherry picked from commit 21d679a)

salt/metalk8s/salt/master/files/master-99-metalk8s.conf.j2

@@ -3,6 +3,8 @@ interface: {{ salt_ip }}
 log_level: {{ 'debug' if debug else 'info' }}
 
 timeout: 20
+sock_pool_size: 15
+worker_threads: 10
 
 peer:
   .*: