Consider adding wasi-runtime-config to proxy world

[lukewagner]

Reading configuration seems like a pretty common use case in the context of HTTP proxies. Now that wasi-runtime-config has made a bunch of progress, we should consider adding import wasi:config/runtime to the proxy world in the next WASI version that includes wasi-runtime-config.

[Mossaka]

Does the dependency on wasi:config/runtime in the proxy world require the WASI Runtime Config proposal to be at least Phase 3 for WASI-HTTP to standardize its interfaces?

[lukewagner]

I suppose so, yeah. IIUC, we could always add it now with @unstable and then switch it over to @since when, presumably in the same WASI 0.2.* release, wasi:config gets voted to Phase 3 and into 0.2.*.