Adding fpp-to-json and fpp tools as CI tests

[mosa11aei]

This was a discussion that was started in nasa/fpp as a PR, but is now moved here after the discussion yielded the idea of having the tests fall in F Prime CI. We pose the idea of adding fpp-to-json and other fpp tools as functional tests in F Prime CI.

1. The nasa/fprime repo is, in majority, a complete model. The RPI and Ref deployments in it provide sample projects which utilize the other fprime-dependent fpp definitions. The expectation is that if the entire nasa/fprime repo cannot be analyzed, then something behaviorally is wrong, either on the F Prime side of things, or the fpp-to-json tool.
2. The repository provides a gold mine of testable semantic patterns and behavioral patterns that would take quite a long time to capture in individual test cases. For example, patterned connection graphs are dependent on Fw (the F Prime framework), which would need to be at least symbolically replicated (i.e., the symbols exist but are gibberish), or (even better) with properly defined symbols. So at that point, why not just go direct to the source?
3. Test cases, especially functional test cases, which are what fpp-to-json and the other tools utilize, are important to ensure that the output analysis matches whatever change occurs. However, in the case of analyzing something as monstrous as the entire nasa/fprime repository, what seems to be a better goal is to verify whether analysis can be done on it. It ensures that F Prime is kept model complete, while also checking the validity of the fpp tools.

Some comments that were made to these rationales were:

is the primary intent to test the validity of the models in nasa/fprime, or to test the fpp-to-json utility itself?

The goal is to do functional testing of the FPP tool on F Prime models, similarly to https://github.com/nasa/fprime/tree/devel/FppTest. Perhaps the fpp-to-json tests could go here.
We could also break out the F Prime-FPP functional testing into a separate repo in fprime-community. In this case we would need to factor FppTest into a separate project that depends on F Prime.

cc @LeStarch @thomas-bc @bocchino