feat: use default config path when no arg for -f is provided #14009

Job	Run time
towncrier_check	7s
check_if_release_branch	2s
changed_files	10s
build mirrord CLI	0s
lint	4m 6s
integration_tests	12m 27s
lint_markdown	0s
check-rust-docs	1m 29s
macos_tests	34m 11s
test_agent	3m 50s
test_agent_image	53s
test_cli_image	16m 2s
e2e (docker)	9m 54s
vscode_e2e_on_release_branch	0s
intellij_e2e_on_release_branch	0s
e2e (containerd)	10m 13s
ci	1s
	1h 33m 25s

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