Support Envoy's allow_on_headers_stop_iteration on wasm PluginConfig

[alexsnaps]

Since Envoy version 1.35, Wasm's PluginConfig, let's you set the allow_on_headers_stop_iteration boolean, which affects how a filter "Pauseing" the request is handled for HTTP request, allowing to proceed to processing the body, while not flushing the buffer with the headers to the upstream.

The control is implemented in the go control plane, "just" not leverage by Istio's WasmPlugin extensions.
There might be a good reason for it to be missing, which is why I'm opening the discussion... or it might just have not yet been implemented/requested or just be an oversight. Would it make sense to add it?

[guicassolato]

Wondering about the state of allow_on_headers_stop_iteration in the new TrafficExtension API. Does its WasmConfig stanza add anything compared to using a WasmPlugin custom resource wrt to controlling the filter flow or they are practically equivalent?