feat: add configurable replicas and antiaffinity to gateway deployment for HA #1210

Job	Run time
Publish Charm / Generate the Charm Matrix	3s
Run Tests / Observability Integration Test (1.25-strict/stable)	38m 21s
Run Tests / Integration Test (1.27-strict/stable, integration)	42m 3s
Run Tests / Observability Integration Test (1.26-strict/stable)	37m 45s
Run Tests / Lint Code (pilot)	22s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-provider)	35m 32s
Run Tests / Lint Code (gateway)	23s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-secret)	39m 14s
Run Tests / Integration Test (1.30-strict/stable, integration)	39m 34s
Run Tests / Unit Test (pilot)	39s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-provider)	35m 54s
Run Tests / Unit Test (gateway)	33s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-secret)	35m 43s
Run Tests / Check libraries (istio-gateway) / Lint	8s
Run Tests / Check libraries (istio-gateway) / Check libraries	28s
Run Tests / Check libraries (istio-pilot) / Check libraries	40s
Run Tests / Check libraries (istio-pilot) / Lint	12s
Run Tests / Terraform (gateway) / Lint Terraform	8s
Run Tests / Terraform (pilot) / Lint Terraform	11s
Run Tests / Terraform (pilot) / Apply / Apply Terraform	5m 7s
Run Tests / Terraform (gateway) / Check / Check Terraform	7s
Run Tests / Terraform (gateway) / Apply / Apply Terraform	6m 4s
Run Tests / Terraform (pilot) / Check / Check Terraform	10s
Publish Charm / Publish Charm (./charms/istio-gateway)	13m 29s
Publish Charm / Publish Charm (./charms/istio-pilot)	17m 24s
	5h 50m 14s

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