fix: Run codejail with app user; more docs (#124) #677

Job	Run time
run_ci (ubuntu-20.04, 3.11, discovery+lms+forum)	21m 25s
run_ci (ubuntu-20.04, 3.11, registrar+lms)	20m 45s
run_ci (ubuntu-20.04, 3.11, ecommerce+lms)	23m 14s
run_ci (ubuntu-20.04, 3.11, edx_notes_api+lms)	16m 58s
run_ci (ubuntu-20.04, 3.11, credentials+lms)	17m 39s
run_ci (ubuntu-20.04, 3.11, xqueue)	3m 26s
run_ci (ubuntu-20.04, 3.11, analyticsapi+insights+lms)	22m 30s
run_ci (ubuntu-20.04, 3.11, designer+lms)	17m 46s
run_ci (ubuntu-20.04, 3.11, enterprise-catalog+enterprise-access+lms)	23m 27s
run_ci (ubuntu-20.04, 3.11, license-manager+lms)	18m 2s
	3h 5m 12s

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