Refactor/simplify the way we define and handle channel, cache and cache-container metrics

Defining metrics per resource via enums simplifies things immensely.
Also, some code cleanup:
* Use consistent class naming for resource definitions and add/remove/describe operation handlers.
* Eliminate superfluous static final values.
* Breakup CacheConfigOperationHandlers into individual add operation handlers for cache stores.
* Traverse model via resource paths where possible.
Can we fix this? other option for this would be to use dummy proxy read only attribute that we used for supporting legacy code. Take a look at ReadResourceNameOperationStepHandler usage