feat: add configurable replicas and antiaffinity to gateway deployment for HA #1194

Job	Run time
Run Tests / Observability Integration Test (1.25-strict/stable)	1h 2m 38s
Publish Charm / Generate the Charm Matrix	3s
Run Tests / Observability Integration Test (1.26-strict/stable)	1h 3m 19s
Run Tests / Integration Test (1.27-strict/stable, integration)	1h 27m 56s
Run Tests / Lint Code (pilot)	21s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-provider)	1h 0m 56s
Run Tests / Lint Code (gateway)	21s
Run Tests / Integration Test (1.27-strict/stable, integration-tls-secret)	1h 2m 10s
Run Tests / Unit Test (pilot)	44s
Run Tests / Integration Test (1.30-strict/stable, integration)	1h 7m 5s
Run Tests / Unit Test (gateway)	37s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-provider)	1h 5m 3s
Run Tests / Integration Test (1.30-strict/stable, integration-tls-secret)	1h 3m 25s
Run Tests / Check libraries (istio-gateway) / Lint	14s
Run Tests / Check libraries (istio-gateway) / Check libraries	30s
Run Tests / Check libraries (istio-pilot) / Check libraries	32s
Run Tests / Check libraries (istio-pilot) / Lint	11s
Publish Charm / Publish Charm (./charms/istio-gateway)	30m 6s
Publish Charm / Publish Charm (./charms/istio-pilot)	41m 9s
	10h 7m 20s

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