Add PMGTruthWeightsAlgCfg, add unit tests for CA code

The non-XAOD_STANDALONE unit tests in this package are using a deprecated configuration system, and a few of the algorithms lacked unit tests. Specifically the tests were missing for PMGTruthWeightAlg, so I'm adding a unit test plus a Cfg function in a python module to set it up like we would any standard algorithm.

While I was doing this I noticed that PileupReweightingAlgConfig already has Cfg function but lacked a test, I'm adding that test too.