chore(cli): create 'gateway' subcommand for network commands #2127

Job	Run time
integration (kong:1.4.3)	1m 37s
integration (kong:1.5.1)	1m 42s
integration (kong:2.0.5)	1m 41s
integration (kong:2.1.4)	1m 52s
integration (kong:2.2.2)	1m 57s
integration (kong:2.3.3)	2m 9s
integration (kong:2.4.1)	1m 44s
integration (kong:2.5.1)	1m 38s
integration (kong:2.6.0)	1m 44s
integration (kong:2.7)	1m 46s
integration (kong:2.8)	1m 48s
integration (kong:3.0)	1m 55s
integration (kong:3.1)	1m 48s
integration (kong:3.2)	1m 53s
integration (kong:3.3)	2m 17s
integration (kong/kong:master-alpine)	2m 5s
	29m 36s

Provide feedback