port over `enqueue/simple-client` #281

Job	Run time
cs-stan / Coding Standard & Static Analysis	27s
testsuite / testsuite-linux (8.1, pgsql, highest, false)	42s
testsuite / testsuite-linux (8.1, mysql, highest, false)	48s
testsuite / testsuite-linux (8.4, mysql, highest, false)	50s
testsuite / testsuite-linux (8.2, mysql, false)	43s
testsuite / testsuite-linux (8.1, sqlite, lowest, false)	39s
testsuite / testsuite-linux (8.3, sqlite, highest, false)	46s
	4m 55s

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