Mark Gateway Injection as Generally Available

Gateway Injection has been officially released in Istio 1.11 upstream. We should mark it as Generally Available for 2.2.0. Gateway injection works in a similar manner to sidecar injection, so all caveats that apply to sidecar injection will also apply to gateway injection, namely:

• Auto-injection is enabled by default upstream, but not by OSSM, which means users will need to add an injection label/annotation to the gateway deployment for injection to occur, when using OSSM defaults
• Injection is disabled in the SMCP namespace, which means that gateway injection will not occur for gateways deployed in the SMCP namespace.

Acceptance Criteria:

• Gateway Injection templates are equivalent in functionality to what is deployed by spec.gateways
• Acceptance tests for mixed gateway deployments (spec.gateways + injected) as well as for only injected gateway deployments
• Documentation on how to use Gateway Injection