Implement /rpc_server_snapshot endpoint

This returns a JSON snapshot of the state of the server

crates/collab/src/main.rs

@@ -104,6 +104,12 @@ impl From<hyper::Error> for Error {
     }
 }
 
+impl From<serde_json::Error> for Error {
+    fn from(error: serde_json::Error) -> Self {
+        Self::Internal(error.into())
+    }
+}
+
 impl IntoResponse for Error {
     fn into_response(self) -> axum::response::Response {
         match self {