feat: add configurable replicas and antiaffinity to gateway deployment for HA #1193

Job	Run time
Publish Charm / Generate the Charm Matrix	5s
Run Tests / Observability Integration Test (1.25-strict/stable)	1h 7m 19s
Run Tests / Integration Test (1.27-strict/stable, integration)	1h 29m 56s
Run Tests / Observability Integration Test (1.26-strict/stable)	1h 5m 30s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-provider)	1h 5m 5s
Run Tests / Lint Code (pilot)	26s
Run Tests / Unit Test (pilot)	40s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-secret)	1h 5m 23s
Run Tests / Lint Code (gateway)	21s
Run Tests / Unit Test (gateway)	31s
Run Tests / Integration Test (1.30-strict/stable, integration)	1h 29m 36s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-provider)	1h 4m 38s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-secret)	1h 4m 47s
Run Tests / Check libraries (istio-gateway) / Check libraries	26s
Run Tests / Check libraries (istio-gateway) / Lint	10s
Run Tests / Check libraries (istio-pilot) / Check libraries	31s
Run Tests / Check libraries (istio-pilot) / Lint	10s
Publish Charm / Publish Charm (./charms/istio-gateway)	30m 32s
Publish Charm / Publish Charm (./charms/istio-pilot)	40m 31s
	10h 46m 37s

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