Require running the rq-worker process

[lampwins]

Environment

• Python version: 3.7
• NetBox version: 2.6.2

Proposed Functionality

Require users to always enable and run the rqworker process as a part of their NetBox installation.

Because of the changes in 2.6 which required Redis and its related dependencies, most of this is just documentation to ensure the rqworker is always running and no longer an optional installation step.

That being said, there is some logic surrounding the WEBHOOKS_ENABLED setting that should be removed which conditionally adds django_rq to the list of installed apps.

Use Case

Making the rqworker process optional has turned out to cause a lot of trouble for new users and creates unnecessary conditional logic in the installation instructions.

Requiring the rqworker to be run, unifies NetBox installations and also opens the door to implementing more background processing features such as #2006, #3351, and more.

Database Changes

None

External Dependencies

Move django-rq to a required dependency. All others became required in 2.6.