Create controlled vocabulary for finemapping methods

[d0choa]

The current finemapping method is currently not constrained to a list of options.

In [36]: df.select("finemappingMethod").distinct().show()
+-----------------+
|finemappingMethod|
+-----------------+
|             pics|
|            SuSie|
|        SuSiE-inf|
+-----------------+

The problem is that we are using the content of this column to make decisions on how we process (e.g. colocalise) and validate the credible sets.

We want to create an Enum that lists all the fine-mapping methods that gentropy considers. This will help us to us a consistent nomenclature and change the labels without impacting the processing.

@addramir, can you confirm the current methods, the desired labels and the sources that use them?