Add default unknown_producer tag value to the producer tag of the StreamingTripUpdateMetrics

[eibakke]

Summary

This PR sets a default value to the producer tag on the prometheus realtime metrics. The current state leaves the producer tag empty when there is no producer on the result, which leads to metrics not updating because prometheus metrics have to have the same tags.

Warning we get currently:

The meter (MeterId{name='streaming_trip_updates.failed', tags=[tag(configRef=SIRI_ET_GOOGLE_PUBSUB_UPDATER),tag(errorType=UNKNOWN),tag(feedId=RB),tag(url=http://realtime-cache.dev.entur.internal/et)]}) registration has failed: Prometheus requires that all meters with the same name have the same set of tag keys. There is already an existing meter named 'streaming_trip_updates.failed' containing tag keys [configRef, errorType, feedId, producer, url]. The meter you are attempting to register has keys [configRef, errorType, feedId, url]. Note that subsequent logs will be logged at debug level.\n

Unit tests

No tests for this part of the code

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 7 lines in your changes missing coverage. Please review.

Project coverage is 70.18%. Comparing base (a555e95) to head (71d1223).
Report is 30 commits behind head on dev-2.x.

Files with missing lines	Patch %	Lines
...dater/trip/metrics/StreamingTripUpdateMetrics.java	0.00%	7 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #6513      +/-   ##
=============================================
- Coverage      70.18%   70.18%   -0.01%     
+ Complexity     18308    18307       -1     
=============================================
  Files           2081     2081              
  Lines          77184    77187       +3     
  Branches        7828     7828              
=============================================
  Hits           54172    54172              
- Misses         20246    20250       +4     
+ Partials        2766     2765       -1     

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[leonardehrenfried]

This looks fine. You say that metrics don't refresh. Does this mean that all metrics hang or just the trip update ones?