Add CI clippy checks for gateway #5604

Job	Run time
check_infra_schema_sync	30s
check_commits	5s
build	6m 21s
check_generated_railjson_sync	26s
check_integration_tests	1m 33s
check_osrd_schema	47s
check_railjson_generator	1m 54s
check_toml	5s
Check final newline	7s
check_editoast_lints	4m 56s
check_editoast_tests	6m 4s
check_editoast_openapi	1m 32s
check_core	3m 56s
check_front_rtk_sync	1m 37s
check_gateway	2m 18s
check_front	2m 19s
integration_tests	4m 40s
	39m 10s

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