Add RD HLT2 lines: Omega to Xi X

The merge request adds several rare Omega lines of Omega -> Xi X:

The signal modes are included:

• Omega -> Xi mu+ mu-
• Omega -> Xi e+ e-
• Omega -> Xi gamma

And the control mode is:

• Omega -> Xi pi+ pi-

Note: Xi decays to Lambda0(-> p pi-) pi and track types include LLL and DDL. Using basic builders from "rdbuilder_thor" and defining a new builder "omega_rare_decay_builder".

FYI @msaur @ziyiw @jfu @xilyu

Rates for HLT2 only based on upgrade_DC19_01_MinBiasMD samples:

----------------------------------------------------------------------------------------------------------------------
Line:	 Hlt2RD_OmegamToXimEE_LLL_LineDecision   	 Incl:     0.0 +/-  0.0 kHz, Excl:     0.0 +/-  0.0 kHz
Line:	 Hlt2RD_OmegamToXimGamma_LLL_LineDecision	 Incl:     0.0 +/-  0.0 kHz, Excl:     0.0 +/-  0.0 kHz
Line:	 Hlt2RD_OmegamToXimMuMu_LLL_LineDecision 	 Incl:     0.0 +/-  0.0 kHz, Excl:     0.0 +/-  0.0 kHz
Line:	 Hlt2RD_OmegamToXimPiPi_LLL_LineDecision 	 Incl:     0.0 +/-  0.0 kHz, Excl:     0.0 +/-  0.0 kHz
----------------------------------------------------------------------------------------------------------------------
HLT2 Total:                                              Rate:     0 +/- 0.0 kHz   
----------------------------------------------------------------------------------------------------------------------

Most lines with a zero rate, and have also tested on the upgrade_minbias_hlt1_filtered sample:

----------------------------------------------------------------------------------------------------------------------
Line:	 Hlt2RD_OmegamToXimEE_LLL_LineDecision   	 #=14983   Sum=0           Eff=|( 0.000000 +- 0.00000 )%|
Line:	 Hlt2RD_OmegamToXimGamma_LLL_LineDecision	 #=14983   Sum=0           Eff=|( 0.000000 +- 0.00000 )%|
Line:	 Hlt2RD_OmegamToXimMuMu_LLL_LineDecision 	 #=14983   Sum=0           Eff=|( 0.000000 +- 0.00000 )%|
Line:	 Hlt2RD_OmegamToXimPiPi_LLL_LineDecision 	 #=14983   Sum=1           Eff=|(0.006674231 +- 0.00667401)%|
----------------------------------------------------------------------------------------------------------------------

Update on 08/06: DDL lines removed due to an absurd_track warnings, rates updated.

requested review from @fevolle, @yafan, @mmulder, and @hvc

assigned to @chuangxi

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• c0615646 - Fixed formatting
• 7361229f - fix formating and change some cuts

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added RD RTA hlt2 selection labels

requested review from @msaur

Hi @chuangxi , thanks for the work. Please make it clear in the description of your full decay chains.

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• 002c2a62 - add default name and modify some cuts

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• e4961671 - Fixed formatting

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