Security: add option to restrict service deployment to node admin

[folex]

Sometimes, node admins want their nodes to be guarded against service deployments by unauthorised users. One of the reasons is resource consumption: unauthorised user could deploy thousands of services and lead node to DoS.

A simple solution to this would be to add optional restriction of srv deploy and dist add_module to admin keys.

That option should be enabled/disabled in the Node Config and CLI arguments.