Support for SST::Statistics handlers in JSON input files

[jleidel]

Is your feature request related to a problem? Please describe.
The current JSON reader/writers for simulation inputs/outputs do not support including statistics directives. It would be ideal for JSON to handle SST::Statistics directives in the same manner as the Python inputs.

Describe the solution you'd like
Add the necessary standard handlers to enable and configure statistics for components, subcomponents, component/subcomponent groups and simulation-wide. This will likely require some notional internal API changes in order to provide sufficient functionality and interoperability.

Describe alternatives you've considered
There aren't really any alternatives if we truly want JSON inputs to be equivalent to Python inputs

Additional context
I can mock up the potential JSON verbiage if need be. Ideally, we'll need:

1. simulation wide statistic enablers
2. component/group enablers
3. per component/subcomponent enablers

[gvoskuilen]

I made assignments so we can track this. If you can mock something up and identify what needs to changed/added, that'd be great.