refactor error handling part 1 (#307)

- created `getErrorMessage` function which takes in an error string or any type of error object and returns the correct error message
- replaced `error.message` with `getErrorMessage` since `error` could be a string in some cases
- merged sendNotificationForError.ts with ErrorHandlingUtils.ts
- some minor refactoring

In part 2, I will make the following changes:
 - Make `Logger.logError` function take an error message string instead of an error object. This will reduce some redundancy where the `getErrorMessage` function is being called twice (the error object passed by the caller is already an error message).
 - Update every `TelemetryProcessor.traceFailure` call to make sure we pass in an error message instead of an error object since we stringify the data we send.

src/workers/upload/index.ts

@@ -3,6 +3,7 @@ import { DocumentClientParams, UploadDetailsRecord, UploadDetails } from "./defi
 import { client } from "../../Common/CosmosClient";
 import { configContext, updateConfigContext } from "../../ConfigContext";
 import { updateUserContext } from "../../UserContext";
+import { getErrorMessage } from "../../Common/ErrorHandlingUtils";
 
 let numUploadsSuccessful = 0;
 let numUploadsFailed = 0;
@@ -93,7 +94,7 @@ function createDocumentsFromFile(fileName: string, documentContent: string): voi
         })
         .catch(error => {
           console.error(error);
-          recordUploadDetailErrorForFile(fileName, error.message);
+          recordUploadDetailErrorForFile(fileName, getErrorMessage(error));
           numUploadsFailed++;
         })
         .finally(() => {