Add functorcollections module to FunTuple framework

Module to provide Functor collections for the FunTuple framework.

It should eventually replace the present NewTupleTools module as it contains some improvements. In particular, it ensures a dynamic construction of the module docstring, as help(functorcollections) shows something like

Help on module functorcollections:

NAME
    functorcollections - Functor collections for the FunTuple framework.

DESCRIPTION
    A typical usage is the following:

    .. code-block:: python

        coll_of_predefined_variables = FunctorCollection(Kinematics)

    List of available collections (with contents):

    Kinematics:
       THOR_MASS      : ::Functors::Composite::Mass{}
       THOR_P         : ::Functors::Track::Momentum{}
       THOR_PT        : ::Functors::Track::TransverseMomentum{}
       THOR_PX        : ::Functors::Track::Px{}
       THOR_PY        : ::Functors::Track::Py{}
       THOR_PZ        : ::Functors::Track::Pz{}
       THOR_E         : ::Functors::Track::Energy{}


DATA
    Kinematics = {'THOR_MASS': ('::Functors::Composite::Mass{}', ['Functor...
    __all__ = ('Kinematics',)

FILE
    /afs/cern.ch/work/e/erodrigu/LHCb/software/Analysis/Phys/FunTuple/python/FunTuple/functorcollections.py

I did not adapt NewTupleTools itself because (1) I do not want to cause disruptions as there's a lot of WIP on the FunTuple framework, (2) a new module allows parallel checks and (3) I find functorcollections a better name :D.

Work on DPA master task https://gitlab.cern.ch/lhcb-dpa/project/-/issues/121. Relates also to https://gitlab.cern.ch/lhcb-dpa/project/-/issues/178.