switch to query error variant that propagates error messages to Graph…

…QL responses (#39)

When we encounter problems with incoming query requests we've been sending back `QueryError::InvalidQuery` error values. But when the engine receives these it produces GraphQL responses that only say "internal error". This change switches to `QueryError::UnprocessableContent`. With this change the engine copies error messages from the connector to the GraphQL response.

crates/mongodb-connector/src/error_mapping.rs

@@ -8,7 +8,7 @@ pub fn mongo_agent_error_to_query_error(error: MongoAgentError) -> QueryError {
     }
     let (status, err) = error.status_and_error_response();
     match status {
-        StatusCode::BAD_REQUEST => QueryError::InvalidRequest(err.message),
+        StatusCode::BAD_REQUEST => QueryError::UnprocessableContent(err.message),
         _ => QueryError::Other(Box::new(error)),
     }
 }
@@ -19,7 +19,7 @@ pub fn mongo_agent_error_to_explain_error(error: MongoAgentError) -> ExplainErro
     }
     let (status, err) = error.status_and_error_response();
     match status {
-        StatusCode::BAD_REQUEST => ExplainError::InvalidRequest(err.message),
+        StatusCode::BAD_REQUEST => ExplainError::UnprocessableContent(err.message),
         _ => ExplainError::Other(Box::new(error)),
     }
 }