Migrate MergeRequestWidgetExtensionCounter to use a Metric Instrumentation class
As a part of #339445 (closed), we want to move the MergeRequestWidgetExtensionCounter from UsageDataCounters
to use basic RedisMetric class, defined with metrics yaml file parameters. This will require moving this class from COUNTERS
to COUNTERS_MIGRATED_TO_INSTRUMENTATION_CLASSES
const in the UsageDataCounters class.
Edited by Michał Wielich