Add Combined slice to joint signatures [ATR-28414]

We seem not to have been attempting to configure any combined chains. This might have been overlooked as the behaviour changed at some point from always having Combined enabled to making it a slice that could be toggled independently.

To make this run, explicit 'MissingCA' steps needed to be added for MinBias: ATR-28356 -- e.g. crashing on empty afpdijet sequences

Other affected signatures have been fixed since this MR was created

• BLS custom ComboHypo enabled by @fpastore, !67066 (merged)
• Change for UTT was moved to !66875 (merged)

With these we should both be able to add the Combined slice in, and get an updated picture of the migration metrics.

[Numbers from earlier in development] Activating this makes the chain count go from 1515 (RDOtoRDOTrig r08) to 1964 for Dev_pp_run3_v1_TrigValidation_prescale.

Currently held up by ATR-28542 -- the hypo seems to be in the wrong sequence, after chain merging. Solution in !67347 (merged).