Add alert rules to istio-gateway based on the KF093 spec #1125

Job	Run time
Publish Charm / Generate the Charm Matrix	2s
Run Tests / Observability Integration Test (1.25-strict/stable)	1h 5m 20s
Run Tests / Integration Test (1.27-strict/stable, integration)	1h 0m 30s
Run Tests / Observability Integration Test (1.26-strict/stable)	1h 17m 37s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-provider)	1h 0m 12s
Run Tests / Lint Code (pilot)	24s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-secret)	1h 0m 35s
Run Tests / Lint Code (gateway)	20s
Run Tests / Unit Test (pilot)	41s
Run Tests / Integration Test (1.30-strict/stable, integration)	1h 0m 31s
Run Tests / Unit Test (gateway)	33s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-provider)	1h 0m 38s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-secret)	1h 0m 32s
Run Tests / Check libraries (istio-pilot) / Check libraries	24s
Run Tests / Check libraries (istio-gateway) / Lint	9s
Run Tests / Check libraries (istio-gateway) / Check libraries	26s
Run Tests / Check libraries (istio-pilot) / Lint	11s
Publish Charm / Publish Charm (./charms/istio-pilot)	40m 13s
Publish Charm / Publish Charm (./charms/istio-gateway)	30m 30s
	9h 39m 48s

Provide feedback