Enable HTTP/2 extended CONNECT from ProxyConfig

[mpuncel]

🤖 Reworked this draft so HTTP/2 extended CONNECT is configured through the ProxyConfig CRD instead of proxy environment metadata.

Summary:

• Consumes API draft Add extended CONNECT setting to ProxyConfig api#2 via a temporary replace istio.io/api => github.com/mpuncel/api ....
• Adds generated CRD schema for ProxyConfig enableHttp2Connect.
• Maps networking.istio.io/v1beta1 ProxyConfig.enableHttp2Connect into effective mesh ProxyConfig.
• Enables http2_protocol_options.allow_connect on sidecar outbound HTTP listeners when effective proxy config enables it.
• Enables the same setting on sidecar inbound HTTP service chains when effective proxy config enables it.
• Does not configure outbound clusters.

Validation:

• go test ./pilot/pkg/networking/core
• go test ./pilot/pkg/model
• go test ./pkg/model -run 'TestNodeMetadata|TestStringBool'
• go test ./pilot/pkg/networking/core -run 'TestOutboundHTTP2ConnectProxyConfig|TestInboundHTTP2ConnectProxyConfig'
• go test ./pilot/pkg/model -run 'TestConvertToMeshConfigProxyConfig|TestEffectiveProxyConfig'
• git diff --check

Note: the temporary API replace should become a normal istio.io/api pseudo-version bump after the fork API PR is merged into the target API branch.