Inclusion of displaced dimuon line with monitoring

One of the requested pieces of follow-up to !1186 (merged) (listed here #424 (closed)) was a monitoring plot of displaced dimuon masses for comparison with HLT2 (cc @gligorov). While adding this, I found that the DisplacedDiMuonLine is not being run at all. After a brief chat with @cmarinbe it was determined that this was probably an error, and so this MR adds DisplacedDiMuonLine to the default physics lines with a monitoring plot.

To aid in the discussion about if it should be included, I'm going to put here a list of the dimuon lines (excluding the SS versions)

line name in HLT1.py	underlying line file name	mass requirements	minIPchi2 cut
DiMuonHighMass	DiMuonMassLine	> 2.7 GeV	N/A
DiMuonLowMass	DiMuonMassLine	N/A	4
DiMuonSoft	DiMuonSoftLine	< 400 MeV or between 475 and 600 MeV	100
LowPtDiMuon	LowPtDiMuonLine	> 220 MeV	1
DiMuonNoIP	DiMuonNoIPLine	N/A	N/A
DiMuonDrellYan_VLowMass	DiMuonDrellYanLine	between 2.9 and 5 GeV	N/A
DiMuonDrellYan	DiMuonDrellYanLine	between 5 and 400 GeV	N/A
DisplacedDiMuon	DisplacedDiMuonLine	> 215 MeV	6

Of course they all have different kinematic cuts as well. There is clearly a lot of overlap here, but none are clear replacements for DisplacedDiMuon. The closest seems to be DiMuonLowMass, but because of the kinematic cuts it does not exactly overlap and would not select all events that DisplacedDiMuon would.