Error reporting improvments

The goal is to provide a platformized way to distinguish between errors at the Fusion layer.

Today, errors are handled in one generic manner. Whether they are client type errors (ie validation, not found) or server type errors (ie authorization, server failures), these errors are logged the same and frontend applications classify them all the same without custom handling.

Having these errors undistinguished creates a difficulty in filtering out specific error types that require different handling. This handling includes alerting on some error types but not others. For example:

Co-authored-by: shYkiSto <siarhei@uber.com>

fusion-plugin-rpc/src/response-error.js

@@ -9,11 +9,29 @@
 export default class ResponseError extends Error {
   code: ?string;
   meta: ?Object;
+  cause: ?mixed;
+  severity: ?$Values<typeof ResponseError.Severity>;
 
-  constructor(message: string) {
+  static Severity = Object.freeze({
+    HIGH: 'HIGH',
+    MEDIUM: 'MEDIUM',
+  });
+
+  constructor(
+    message: string,
+    options?: ?{
+      code?: string,
+      meta?: Object,
+      cause?: mixed,
+      severity?: $Values<typeof ResponseError.Severity>,
+    }
+  ) {
     super(message);
-    this.code = null;
-    this.meta = null;
+    const {code, meta, cause, severity} = options ?? {};
+    this.code = code;
+    this.meta = meta;
+    this.cause = cause;
+    this.severity = severity;
     Error.captureStackTrace(this, ResponseError);
   }
 }

fusion-plugin-rpc/src/server.js

@@ -214,7 +214,9 @@ const pluginFactory: () => RPCPluginType = () =>
                 e instanceof ResponseError
                   ? e
                   : new Error(
-                      'UnknownError - Use ResponseError from fusion-plugin-rpc (or fusion-plugin-rpc-redux-react if you are using React) package for more detailed error messages'
+                      __DEV__
+                        ? 'UnknownError - Use ResponseError from fusion-plugin-rpc (or fusion-plugin-rpc-redux-react if you are using React) package for more detailed error messages'
+                        : 'Internal Server Error'
                     );
               ctx.body = {
                 status: 'failure',