Replace remaming usage of pkg_resources in doc build #871

Job	Run time
doc (docs)	1m 39s
check (build)	51s
doc (docs-gnocchi-web)	2m 10s
check (pep8)	48s
test (py39, postgresql-file-upgrade-from-4.5)	2m 43s
test (py39, mysql-file)	3m 8s
test (py39, mysql-file-sqlalchemy14)	2m 59s
test (py39, mysql-swift)	3m 36s
test (py39, mysql-s3)	4m 2s
test (py39, postgresql-file)	3m 1s
test (py39, postgresql-file-sqlalchemy14)	2m 47s
test (py39, postgresql-swift)	3m 15s
test (py39, postgresql-s3)	3m 44s
test (py311, postgresql-file-upgrade-from-4.5)	2m 35s
test (py311, mysql-file)	2m 54s
test (py311, mysql-file-sqlalchemy14)	2m 51s
test (py311, mysql-swift)	3m 34s
test (py311, mysql-s3)	3m 55s
test (py311, postgresql-file)	2m 49s
test (py311, postgresql-file-sqlalchemy14)	2m 45s
test (py311, postgresql-swift)	3m 16s
test (py311, postgresql-s3)	3m 17s
test (py312, mysql-ceph-upgrade-from-4.5)	2m 32s
test (py312, postgresql-file-upgrade-from-4.5)	2m 36s
test (py312, mysql-file)	3m 7s
test (py312, mysql-file-sqlalchemy14)	2m 58s
test (py312, mysql-swift)	3m 17s
test (py312, mysql-s3)	3m 37s
test (py312, postgresql-file)	2m 42s
test (py312, postgresql-file-sqlalchemy14)	2m 39s
test (py312, postgresql-swift)	3m 13s
test (py312, postgresql-s3)	3m 38s
	1h 32m 58s

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