`filewriter`: decide where histogramming needs to occur

Histogram mode files are looking like they are a requirement for HRPD-X.

We need to decide at what point in the pipeline:
A) TCBs are actually specified for a histogram
B) A histogram file is created

We may be able to do this _after_ and event mode file is created, ie. by the filewriter, using a service like the FIA. Alternatively we could do it in the filewriter.

The streaming hardware does not currently have the capability to stream histograms so this should not be a consideration. It also becomes more of a challenge for propagating TCBs.

Start by tracing the pipeline points where TCBs are specified and where histogram files are created. Compare the filewriter path with the FIA-based alternative, keeping the streaming hardware limitation in scope. Done means the project has a decided location for histogramming and a clear approach to propagating TCBs.

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