Add metrics-endpoint to istio-gateway #1072

Job	Run time
Run Tests / Observability Integration Test (1.25-strict/stable)	1h 0m 50s
Publish Charm / Generate the Charm Matrix	3s
Run Tests / Integration Test (1.27-strict/stable, integration)	1h 15m 22s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-provider)	57m 57s
Run Tests / Observability Integration Test (1.26-strict/stable)	1h 4m 10s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-secret)	56m 17s
Run Tests / Unit Test (pilot)	46s
Run Tests / Integration Test (1.30-strict/stable, integration)	1h 15m 40s
Run Tests / Lint Code (pilot)	24s
Run Tests / Unit Test (gateway)	36s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-provider)	56m 47s
Run Tests / Lint Code (gateway)	24s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-secret)	55m 57s
Run Tests / Check libraries (istio-gateway) / Check libraries	27s
Run Tests / Check libraries (istio-pilot) / Check libraries	25s
Run Tests / Check libraries (istio-gateway) / Lint	10s
Run Tests / Check libraries (istio-pilot) / Lint	9s
Publish Charm / Publish Charm (./charms/istio-pilot)	38m 16s
Publish Charm / Publish Charm (./charms/istio-gateway)	27m 34s
	9h 32m 14s

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