stats: add feature flag for indexing stats data onto records #1296

Job	Run time
Tests (ill, 3.9, pypi, postgresql14, opensearch2)	4m 8s
Tests (ils, 3.9, pypi, postgresql14, opensearch2)	16m 35s
Tests (circulation, 3.9, pypi, postgresql14, opensearch2)	8m 53s
Tests (document_requests, 3.9, pypi, postgresql14, opensearch2)	3m 21s
Tests (acquisition, 3.9, pypi, postgresql14, opensearch2)	2m 42s
	35m 39s

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