Add test for json_each + json_keys. #701

Job	Run time
Build and Test PowerSync Service	1m 22s
Core Test	1m 26s
MongoDB Test (6.0)	2m 11s
MongoDB Test (7.0)	2m 5s
MySQL Test (5.7)	1m 39s
MongoDB Test (8.0)	2m 2s
Postgres Test (11)	6m 47s
MySQL Test (8)	1m 41s
Postgres Test (12)	7m 0s
Postgres Test (13)	6m 31s
MySQL Test (8.4)	1m 40s
Postgres Test (14)	6m 43s
Postgres Test (15)	6m 29s
Postgres Test (16)	6m 24s
	54m 0s

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