Overload HASH transfrom to cheat checks

[Jonathan-Poelhuis]

I took an easy route, and (using the idea of Damien) overloaded the HASH transform to get past pipelinewise strict hard-coded checking (that also relies on another external package.) Different from Damien's approach, I wrote the new transforms in the transform_utils.py rather than try an "import a package of our own" approach. It's less snappy but potentially simpler.

To make this work, I

• Added optional external_type and param to the tap.json schema
• Added parsing of those optional parameters to the config.py (including levels when they're missing)
• Added a ExternalTransformationType Enum, including valid levels for when the parameters are not given
  • Then overloaded the TransformationType.HASH to have a switch when an external_type is given.
  • The example functions here are just examples to demonstrate how the code should work.