feat: add configurable replicas and antiaffinity to gateway deployment for HA #1195

Job	Run time
Publish Charm / Generate the Charm Matrix	2s
Run Tests / Integration Test (1.27-strict/stable, integration)	1h 35m 8s
Run Tests / Observability Integration Test (1.25-strict/stable)	1h 2m 32s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-provider)	1h 2m 6s
Run Tests / Observability Integration Test (1.26-strict/stable)	1h 3m 45s
Run Tests / Lint Code (pilot)	20s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-secret)	1h 0m 56s
Run Tests / Unit Test (pilot)	39s
Run Tests / Lint Code (gateway)	35s
Run Tests / Integration Test (1.30-strict/stable, integration)	1h 8m 20s
Run Tests / Unit Test (gateway)	34s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-provider)	1h 3m 5s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-secret)	1h 6m 12s
Run Tests / Check libraries (istio-pilot) / Check libraries	25s
Run Tests / Check libraries (istio-gateway) / Check libraries	32s
Run Tests / Check libraries (istio-gateway) / Lint	11s
Run Tests / Check libraries (istio-pilot) / Lint	11s
Publish Charm / Publish Charm (./charms/istio-gateway)	30m 4s
Publish Charm / Publish Charm (./charms/istio-pilot)	39m 47s
	10h 15m 24s

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