Draft: Add a Z->mumu line for possible lumi monitoring

Adds OS and SS Z->mumu lines that require a vertex with two high-pT muons. The rate on minbias data is essentially zero (no events passed in the samples available) but in theory this is a very loose cut for true Z->mumu events.

Dependent on !664 (closed) and !784 (closed) as this has to run without the GEC. Once those are merged, the rate reduction should be fixed.

The plan is to add monitoring histograms of the dimuon mass to both of these lines to allow luminosity to be determined. These will probably come in a separate MR to avoid also adding a dependency on !641 (closed).