providers/proxy: fix traefik label generation #24561

Job	Run time
lint-golint	45s
test-unittest	3m 47s
ci-outpost-mark	1s
build-container (proxy)	2m 23s
build-container (ldap)	2m 6s
build-binary (proxy, linux, amd64)	1m 53s
build-container (radius)	2m 15s
build-binary (proxy, linux, arm64)	1m 57s
build-container (rac)	2m 1s
build-binary (ldap, linux, amd64)	2m 1s
build-binary (ldap, linux, arm64)	1m 57s
build-binary (radius, linux, amd64)	1m 51s
build-binary (radius, linux, arm64)	2m 4s
build-binary (rac, linux, amd64)	1m 39s
build-binary (rac, linux, arm64)	2m 5s
	28m 45s

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