Add StrippingBc2Ds2MuMuLine

Added line for Bc+ -> Ds2* (-> D0 (-> K- pi+) K+) mu+ mu- decay, in addition SSLine is added too.

Rates and timing results for 2018:

StrippingReport                                                INFO Event 10000, Good event 10000
 |                                              *Decision name*|*Rate,%*|*Accepted*| *Mult*|*ms/evt*|
 |_StrippingGlobal_                                            |  0.0100|         1|       |   4.865|
 |_StrippingSequenceStreamDimuon_                              |  0.0100|         1|       |   4.856|
 |!StrippingBc2Ds2MuMuLine                                     |  0.0100|         1|  1.000|   3.920|
 |!StrippingBc2Ds2MuMu_SSLine                                  |  0.0000|         0|  0.000|   0.128|
 |!StrippingBc2Ds2MuMuLine_TIMING                              |  0.0100|         1|  1.000|   0.023|
 |!StrippingBc2Ds2MuMu_SSLine_TIMING                           |  0.0000|         0|  0.000|   0.027|

TBD:

• tune the rate
• check the efficiency on MC

Updated rates and timing results (for 2018) on 17/Jul/2023:

StrippingReport                                                INFO Event 100000, Good event 100000
 |                                              *Decision name*|*Rate,%*|*Accepted*| *Mult*|*ms/evt*|
 |_StrippingGlobal_                                            |  0.0140|        14|       |   5.176|
 |_StrippingSequenceStreamDimuon_                              |  0.0140|        14|       |   5.163|
 |!StrippingBc2Ds2MuMuLine                                     |  0.0100|        10|  1.200|   4.085|
 |!StrippingBc2Ds2MuMu_SSLine                                  |  0.0050|         5|  1.200|   0.155|
 |!StrippingBc2Ds2MuMuLine_TIMING                              |  0.0100|        10|  1.200|   0.042|
 |!StrippingBc2Ds2MuMu_SSLine_TIMING                           |  0.0050|         5|  1.200|   0.030|