Use pbjson_build to ensure that proto types have Serialize, Deserialize impls compatible with ProtoJSON

[hdevalence]

It's useful to be able to serialize and deserialize ProtoJSON. This can only be done together with the proto codegen, not by downstream users, so it happens in the ibc-proto crate or not at all.

To do it, the pbjson_build crate could be hooked into the proto compiler; an example can be found in the Penumbra repo: https://github.com/penumbra-zone/penumbra/blob/main/tools/proto-compiler/src/main.rs#L47 This also involves changing the WKTs to ones that support ProtoJSON, so it's definitely a breaking change.

[hdevalence]

It looks like this was done in #92, but not yet released. I see an 0.31.0-alpha.2 tag; is there any reason not to release it as 0.31?

[romac]

The initial idea was to give @Wizdave97 and others time to make sure that these changes work for them. It then fell under our radar, sorry about that. I think it's indeed time to do a final release now. I'll get on it!

[romac]

Done in #92 and released in v0.31.0.

[hdevalence]

Amazing, thanks!