Adds additional rake task to clear jobs from a specific queue

[azeezahmed]

Currently, the 'jobs:clear' task clears all the records from the delayed_job table however, there will be scenarios where jobs only from a specific queue need to be cleared.

ex: restarting (post-maintenance) you would only want to clear WebSocket jobs (news feed) but not subscription charges job (monthly billing).

this pull request adds an additional rake task that accepts a parameter(queue_name) and clears the jobs from the queue.