3157 use enum labels in current filters search status

[harunkumars]

Fixes Issue activeadmin#3157 - Display Enum labels for Active Filters in Current Search Status

ActiveAdmin::Filters::ActiveFilter#values controls the displayed value for active filters.
This currently does not have any special handling for Enums.

For e.g. with an enum definition like enum status: [:inactive, :active] , when filtering for :inactive status, the Current Search Status widget shows "Status is 0"

This PR, uses ActiveRecord::Enum.defined_enums to translate the display value for the filter to the associated label for enums. The Current Search Status widget will now show "Status is Inactive"

If a custom collection is provided when registering the ActiveAdmin resource e.g. filter :status, as: :select, collection: [[:not_active, 0], [:active, 1]] which specifies dropdown labels that are different from the enum labels, then the dropdown label from the custom collection is used. The Current Search Status widget will now show "Status is Not Active"

[npgretz]

Just wanted to add this is very much still a desired feature for me! I explained another work around with Enumerize in my comment on this closed thread: activeadmin#3157 (comment)