Allow Parameter Value selection in AssayGraph dict

[proccaserra]

considering an AssayGraph dictionary (e.g. ms_assay_dict as found in test_create_models_study_design.py), which defines protocol parameters, each with n options,
the code currently creates the cross-products over all values of each set.

improvement:
allow selection of a subset of value for each parameter, thus reducing the number of combinations.

template definition:
parameter=acquisition_mode, values = [positive mode, negative mode]
parameter=injection_mode, values = [FIA,GC,LC]
(current behaviour = create all possible combinations)

user setting for the assay plan:
parameter=acquisition mode, values = [positive mode]
parameter=injection_mode, values = [GC,LC]
(desirable behaviour = allow user to restrict the space to only those relevant to need)