Add extra vars functionality (#37) #24

Job	Run time
opensips / setup-matrix	4s
opensips / test (accounting, ubuntu-latest)	1m 50s
opensips / test (auth, ubuntu-latest)	2m 8s
opensips / test (b2b, ubuntu-latest)	6m 29s
opensips / test (dialog, ubuntu-latest)	2m 37s
opensips / test (permissions, ubuntu-latest)	1m 8s
opensips / test (presence, ubuntu-latest)	52s
opensips / test (record-route, ubuntu-latest)	53s
opensips / test (registration, ubuntu-latest)	4m 14s
opensips / test (startup, ubuntu-latest)	1m 16s
opensips / test (stir-shaken, ubuntu-latest)	5m 2s
opensips / test (topology-hiding, ubuntu-latest)	2m 55s
opensips / test (uac-auth, ubuntu-latest)	3m 0s
	32m 28s

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