[FEATURE] add database as a driver for queues

[vinayak25]

Feature Description

1. Now we can use database as a queue. This will be useful for projects which are MVP or don't want to scale immediately.

Minor Improvements

1. Now the delay attributes will accept, either a number, strings (eg "2days", "72h"), or else a Date object which is future based.
2. Did some code refactoring, moved all of the job classes to a single file in queue/interfaces/job.ts