Add function in RD isolation for vertex isolation online selection of 2-body and 3-body combinations

Add a simple function in rd_isolation to save as extra_outputs two-body and three-body combinations under specific conditions.

• Two-body combinations are persisted if the absolute value of the DELTACHI2 between the combination and the reference particle is smaller than max_two_body_vtx_cut (default: 9);
• Three-body combinations are persisted if the absolute value of the DELTACHI2 between the combination and the reference particle is smaller than make_three_body_combination (default: 15);

Application example in some LFV lines B->K*taul.

Primarily inspired by the work done by @amathad in DaVinci!955

A small modification on the isolation method affects charm implementation (cc: @smaccoli). Trivial modifications are applied.

cc: @mvesteri, @poluekt