feat(jsonrpc): generate OpenRPC definitions

When running `cargo test` in the deltachat-jsonrpc folder,
a new file `openrpc/openrpc.json` will be created with an
[OpenRPC](https://spec.open-rpc.org/) definition.

It can be copy-pasted into the
[OpenRPC playground](https://playground.open-rpc.org/)
and used to generate clients in other languages.

deltachat-rpc-server/Cargo.toml

@@ -21,7 +21,7 @@ serde_json = "1.0.96"
 serde = { version = "1.0", features = ["derive"] }
 tokio = { version = "1.28.0", features = ["io-std"] }
 tokio-util = "0.7.8"
-yerpc = { version = "0.4.0", features = ["anyhow_expose"] }
+yerpc = { version = "0.5.1", features = ["anyhow_expose"] }
 
 [features]
 default = ["vendored"]