Add `map` for `ServiceConfig` #2755

Job	Run time
test (examples)	7m 12s
test (utoipa)	1m 0s
typos	5s
test (utoipa-gen)	2m 35s
test (utoipa-swagger-ui-vendored)	8s
test (utoipa-swagger-ui)	3m 14s
test (utoipa-redoc)	1m 42s
test (utoipa-rapidoc)	1m 25s
test (utoipa-scalar)	1m 19s
test (utoipa-axum)	48s
test (utoipa-config)	49s
test (utoipa-actix-web)	1m 8s
	21m 25s

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