TRExtractor fixes

[mroda88]

While using TRExtractor at EHN1 I noticed two issues:

• Failed start at second start. I tried a the following transition sequences:
  start -> stop -> start (without reconfiguring). In the second run the TRExtractor was not sending request

• The TRExtractor monitoring does not report the number of the received TR, it would be nice to add it

[eflumerf]

For your second bullet, the TRMonRequestor does not receive the TriggerRecords. You should look at the DataWriter "records_received" metric from the TRMonReqApplication.

[mroda88]

DataWriter plots has been added in the DQM dashboard with DUNE-DAQ/grafana-dashboards#112. With this the Issue can be closed.