feat: replace grpc-js with grpc-web for clients

[pfletcherhill]

No description provided.

[kcchu]

I took a look at this but I am not sure about the target of this issue. grpc-web is a different protocol than grpc. grpc uses HTTP/2 special features that are hard to be supported by browser clients. What grpc-web do is defining a protocol that is compatible with HTTP and browser clients and convertible to grpc. It seems to me that hub rpc is primarily server-to-server, and the case for browser clients to call hub rpc directly is very rare. (web apps usually use higher level Merkle API instead) Also, the support for grpc-web in language other than JS is very bad. Therefore, I think grpc+flatbuffer seems to be a better choice for hub rpc.

[pfletcherhill]

Based on some experimentation, it seems like hubs can support both grpc and grpc-web if we host a proxy to translate between the grpc-web HTTP and grpc HTTP/2 calls. That would allow other hubs or backends to communicate with the hubs over grpc and also let devs build client-only apps that use grpc-web. So this issue is not actually replacing grpc-js with grpc-web, we just want to add support for grpc-web. Going to close this issue in favor of the other linked issue #573.