OpenLibrary API proxy example

[emcfarlane]

OpenLibrary use a live books API to demo mapping RPC->REST.

The search service returns duplicate fields: num_found, at the top and bottom of a list. This fails with protojson: golang/protobuf#1568
It would be useful for implementations to handle route by route mutations. Currently using the proxy to mutate request/respons. I think to support all the weirdness of REST apis we will have to give users lots of flexibility on translating.

Stripe

I didn't realize stripe doesn't accept JSON on POST... only url encoded values using their custom syntax: https://stripe.com/docs/api/payment_intents/create . See the first commit.

So this example is a dead end. It surprisingly works for creating and getting a payment intent if you don't use any fields with an _, but anything more complex won't be possible.

[jhump]

We can revisit this later -- likely something in connectrpc/examples-go repo.