NEW AdminController as superclass for /admin/* routed controllers #1633

Job	Run time
CI / Generate matrix	11s
CI / Context	1s
CI / 8.3 prf-low mariadb phpunit all	1m 43s
CI / 8.3 mysql80 phpunit all	1m 34s
CI / Check governance	0s
CI / 8.3 mysql80 phplinting	1m 17s
CI / 8.3 mysql80 endtoend root job1	2m 40s
CI / 8.3 mysql80 endtoend root job2	2m 50s
CI / 8.3 mysql80 endtoend root job3	3m 39s
CI / 8.3 mysql80 js	1m 16s
CI / Dispatch tag patch release	0s
	15m 11s

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