Add discarded flag to digitiser aggregator spans (#309) #1103

Job	Run time
Formatting and Quality	5m 19s
Components (diagnostics) / Build	15s
Components (nexus-writer) / Build	21s
Components (digitiser-aggregator) / Build	5m 0s
Components (simulator) / Build	21s
Components (trace-archiver-hdf5) / Build	17s
Components (trace-archiver-tdengine) / Build	13s
Components (trace-reader) / Build	22s
Components (trace-to-events) / Build	14s
	12m 22s

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