Allow agent port to be configurable #14080

Job	Run time
towncrier_check	11s
check_if_release_branch	1s
changed_files	11s
build mirrord CLI	0s
integration_tests	12m 20s
lint	12m 14s
check-rust-docs	4m 24s
lint_markdown	0s
macos_tests	32m 21s
test_agent	3m 23s
test_cli_image	15m 33s
test_agent_image	6m 24s
e2e (docker)	14m 23s
vscode_e2e_on_release_branch	0s
e2e (containerd)	14m 54s
intellij_e2e_on_release_branch	0s
ci	1s
	1h 56m 20s

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