PMM-14958 Fix duplicate metrics errors

[ademidoff]

SUBMODULES-4286

This pull request enhances the support for monitoring MySQL group replication with parallel replication workers. It updates the custom queries and their corresponding tests to include the worker_id label, which allows metrics to be reported separately for each replication worker thread. This change improves observability in environments where parallel replication is used.

Key changes:

Custom Query Enhancements:

• Updated the mysql_perf_schema_replication_group_worker and mysql_perf_schema_replication_group_worker_5 queries in both queries-mysqld-group-replication.yml and percona/tests/custom-queries/high-resolution/queries-mysqld-group-replication.yml to select and expose the worker_id field, enabling per-worker metrics. [1] [2]
• Added the worker_id label to the metrics definitions, with descriptions clarifying its meaning for both single-threaded and parallel replication scenarios. [1] [2]

Testing Improvements:

• Added a new unit test (TestScrapeCustomQueriesReplicationGroupWorkerParallelReplication) in collector/percona_custom_query_test.go to verify that metrics are correctly produced for each parallel replication worker, ensuring the new worker_id label is handled as expected.

These changes improve the accuracy and granularity of replication monitoring for MySQL instances using group replication with parallel workers.