/publish endpoint enhancements and handling for pass-through subscriber

- new get and post endpoints for /publish/:id/.* where the .* is passed as a data member to the subscribers for handling
- pass-through is now configurable such that one can specify the type of HTTP call made (defaults to POST)
- pass-through is now configurable to, if extra path data is found, add the extra path information to the end of the callback url
- test coverage for scenarios above as well as config validator logic in pass-through