This allows us to specify a feature category on controller
actions.

To specify a feature category can be specified on an entire controller
using:

  feature_category :source_code_management

The feature category can be scoped to a list of actions using the
`only` argument, actions can be excluded using the `except` argument.

  feature_category :source_code_management, only: [:create, :update]
  feature_category :source_code_management, except: [:metrics_reports]

`except` and `only` arguments can not be combined. When specifying
`unless` all other actions will get the category assigned.

The assignment can also be scoped using `if` and `unless` procs:

  feature_category :source_code_management,
                   unless: -> (action) { action.include?("reports") }
                   if: -> (action) { action.include?("widget") }

In this case, both procs need to be satisfied for the action to get
the category assigned.

The `spec/controllers/every_controller_spec.rb` will iterate over all
defined routes, and check the controller to see if a category is
assigned to all actions. The spec also validates if the used feature
categories are known. And if the actions used in `only` and `except`
configuration still exist as routes.