REP-77-XSD Validate service name in service list

This is the version of REP-77 that uses an XSD enumeration rather than code to perform the service name check. By forcing this restriction in the XSD, we are able to leverage our current configuration management code. Additionally, since Repose does not currently support custom services, adding code complexity for no functional gains seems like pre-optimization.

This is not the most optimal or final solution. It does, however, achieve our current goals with incredibly minimal overhead.

Reference #983 for the system model listener solution.