Add Service Definition Management to Admin API

Currently, the Admin API allows management and access to topologies, descriptors, provider config, etc but does not provide access to the Service Definitions for the proxied services.

Let's expand the API the include to include service defs and allow for customization through the API. Changes made via the API will typically require a restart and touch of an topology file that is referencing the change service def. This may require a separate Jira and effort to address. In the meantime, we should be able to change, add and delete service definitions including both service and rewrite XML files.