[DOC] Add clarification for metrics summary and traceQL metrics #9588

Job	Run time
Lint	3m 19s
Benchmark	9m 29s
Build	1m 46s
Build technical documentation	21s
Run integration tests (test-e2e)	20m 34s
Run integration tests (test-integration-poller)	9m 58s
Check jsonnet & tempo-mixin	53s
Vendor check	1m 21s
Run integration tests (test-e2e-deployments)	13m 17s
Run Unit Tests (test-with-cover-pkg)	3m 8s
Run integration tests (test-e2e-serverless)	6m 58s
Run Unit Tests (test-with-cover-tempodb)	15m 44s
Run Unit Tests (test-with-cover-tempodb-wal)	11m 26s
Run Unit Tests (test-with-cover-others)	12m 19s
	1h 50m 33s

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