Security/privacy considerations around did:onion

[clehner]

As mentioned in https://github.com/spruceid/ssi/pull/147:

Security considerations around use in browsers: should some safety be placed around this resolver in WASM usage? In non-WASM, the default is to use proxy 127.0.0.1:9050, but in the browser there is no such assumption - we just fire off a Fetch reqwest.