refactor: move database client to test #15680

Job	Run time
Check typos and docs	15s
Check (windows-latest)	10m 56s
Check (ubuntu-20.04)	1m 49s
Clippy	3m 0s
Toml Check	34s
Build GreptimeDB binaries (ubuntu-20.04)	6m 31s
Rustfmt	39s
coverage	13m 37s
Sqlness Test (ubuntu-20.04)	2m 39s
Fuzz Test (fuzz_create_table)	4m 57s
Sqlness Test with Kafka Wal (ubuntu-20.04)	3m 11s
Fuzz Test (fuzz_alter_table)	5m 26s
Fuzz Test (fuzz_create_database)	5m 13s
Fuzz Test (fuzz_create_logical_table)	5m 26s
Fuzz Test (fuzz_alter_logical_table)	5m 20s
Fuzz Test (fuzz_insert)	5m 23s
Fuzz Test (fuzz_insert_logical_table)	4m 56s
	1h 19m 52s

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