refactor: Prefer use of RequestError and next() function on middlewares

Added:
- New error types such as `IntegrationNotFoundError`,
  `WorkspaceNotFoundError`, `AccountNotFoundError' and more.

Refactored:
- Refactored most of the middlewares and very little number of helper
  functions to use RequestError
- Deleted unused imports

Changed:
- Some of the error types in middlewares changed to more related error
  types.
- Environment variable of 'VERBOSE_ERROR_OUTPUT' changed to more
  reliable validation method in `config/index.ts` as per @dangtony98
  requested.

backend/src/middleware/requireServiceTokenAuth.ts

@@ -1,6 +1,5 @@
 import jwt from 'jsonwebtoken';
 import { Request, Response, NextFunction } from 'express';
-import * as Sentry from '@sentry/node';
 import { ServiceToken } from '../models';
 import { JWT_SERVICE_SECRET } from '../config';
 import { BadRequestError, UnauthorizedRequestError } from '../utils/errors';
@@ -42,7 +41,7 @@ const requireServiceTokenAuth = async (
 		.populate('user', '+publicKey')
 		.select('+encryptedKey +publicKey +nonce');
 
-	if (!serviceToken) return next(UnauthorizedRequestError({message: 'Failed to locate Service Token'}))
+	if (!serviceToken) return next(UnauthorizedRequestError({message: 'The service token does not match the record in the database'}))
 
 	req.serviceToken = serviceToken;
 	return next();