Add ping pong subtask to extproxy (#3039) #14025

Job	Run time
check_if_release_branch	1s
towncrier_check	8s
changed_files	10s
build mirrord CLI	0s
test_agent	4m 16s
test_agent_image	7m 8s
integration_tests	13m 43s
lint	3m 27s
check-rust-docs	59s
macos_tests	24m 0s
test_cli_image	15m 32s
lint_markdown	0s
e2e (docker)	16m 15s
e2e (containerd)	6h 0m 1s
intellij_e2e_on_release_branch	0s
vscode_e2e_on_release_branch	0s
ci	1s
	7h 25m 41s

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