Exposing Wasm VM state in a health check endpoint

Title: Exposing Wasm VM state in a health check endpoint

Description: Any unrecoverable error in the Wasm VM will panic it, and all coming requests will get 503. Users have to reload the wasm filter or restart the envoy process to eliminate the issue.

I didn't find any specific mechanism/API from Envoy documents that can help users identify the status of the Wasm VM. This is useful for building a liveness probe to have the envoy process restart without any human interaction.

Thank you!