It would be useful to have an EPICS channel to note when the daqd is 'stuck' for a long time waiting on data

When the daqd starts up the screens go 'green' and status values go good as the default value is 0. However is data is not flowing to the daqd it is stuck at the current uptime. This can be detected by looking for changes in uptime, but it would be nice to have a signal from the producer thread to say data has not arrived in over X seconds, we are stuck/stale/...

It is proposed to add epics value to the daqd that is normally at '0', but goes to '1' (or higher) if the producer does not see data after a significant amount of time (which could be as small as 1s for daqd work).