Add native support of Observe-SDK in wasmtime runtime

As discussed over a mail thread, if someone wants to monitor their wasmplugins running inside Envoy proxy which uses Wasmtime runtime, atm observe-sdk can't be used because the runtime is the default one and we can't modify it to have the observe-sdk embedded into it.
Similar scenario happens when we use spin, since spin also uses wasmtime as wasm runtime.

One thing we can do that came out of a discussion with @nilslice is that, we can integrate observe-sdk in wasmtime and create/maintain a fork of wasmtime with builtin observe-sdk.

This issue is to track the discussion/work around this.