Support c++ sdk

The wasm go sdk has been deprecated, that repo owner recommends to using c++/rust sdk.
I have tested the example of c++ sdk repo, it's not work. The nginx has loaded my wasm plugin (log in error.log), but it not printed log message in functions, just like instances of my plugin has not be registered. The sdk provides an instance registration mechanism, but the strange thing is that after I commented out this line of code, the proxy behavior of nginx did not change at all, and neither did the error.log

[example](https://github.com/proxy-wasm/proxy-wasm-cpp-sdk/blob/main/example/http_wasm_example.cc)

[registration mechanism](https://github.com/proxy-wasm/proxy-wasm-cpp-sdk/blob/main/docs/api_overview.md#registering-contexts)

nginx.conf:
```
worker_processes auto;
error_log error.log info;

events {}

wasm {
backtraces on;
module request_recorder /home/zhangnf/workspace/codes/cpp/proxy-wasm-cpp-sdk/artifact/http_wasm_example.wasm;
}

http {
server {
listen 19052;

location / {
proxy_wasm request_recorder;
proxy_pass http://bing.com;
}
}
}
```

Reproduce the issue with the provided nginx.conf and the example/http_wasm_example.cc example. Read the registration mechanism in docs/api_overview.md, then inspect error.log while testing whether the configured request_recorder instance receives requests. Done means the C++ SDK example is registered and its function log messages appear through the nginx module.

Written by the indexing model from the issue text.