[Backport 1.8.latest] Add `get_catalog_for_single_relation` to `MockAdapter` #11722

Job	Run time
integration test metadata generation	1s
Test Log Schema (1)	3m 35s
Test Log Schema (2)	2m 43s
Test Log Schema (3)	3m 16s
Test Log Schema (4)	3m 33s
Test Log Schema (5)	4m 1s
Log Schema Test Suite	1s
	17m 10s

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