add a addPrivateToolInArray function to DualUseConfig.py

Unfortunately I don't have a really good way to test if it works, but the underlying C++ is tested, and this is hopefully a close enough duplication of what's happening for non-array tools that this is good enough.

Originally I tried to do something more involved, but that became sort of tedious given the logic of the python class. Maybe at some point I will come back and restructure the python class somewhat. Hopefully this is still workable as is.

cc @delsart @khoo @wbalunas (who asked for dual-use ToolHandleArray support for the jet group)

cc @akraszna (who originally wrote the python AnaAlgorithmConfig)