gRPC-Web Integration

[sgammon]

Currently, grpc-web requires a middleman proxy to function against Java servers. That's because the browser doesn't yet talk pure gRPC, sure there is a slightly different protocol which must be mediated between the browser and backing gRPC server.

It would be really cool if we could run this layer within the JVM, where we wouldn't have to jump a network boundary or run a separate process.

Future considerations:

• Not full parity with ESPv2. Later, we could consider adding API key checking and quota tracking, etc.
• No authorization. JWT authorization is handled by Micronaut in general; integrating with that is ideal
• Client-side code. To do this properly, we'd either need to code-gen bindings (which requires two layers of translation), or we need to get creative and integrate in a deeper way with the new asset system. Later work for sure.