Revamp the promotions admin list using a view

Describe your bug or feature request.

Currently the admin promotions list is powered by a simple entity list builder. One reason why this was never converted to a view was the draggable rows allowing to specify the promotions order.

As a result, it's currently impossible to easily add filters, sorts etc...

For example, we can't currently filter by coupon code, offer, or even name. All of this would be easily doable if the list was powered by a view.

Unfortunately, we can't easily add drag&drop support to the view without depending on yet another contrib module (e.g draggableviews).

My proposal is to replace the current list by a view, and move the current listing under a "Reorder" tab.

This way, we'd have a first tab listing all promotions with filters etc, and a second list where users can tweak the promotions order.

This gives us the following:

I'm also suggesting we revert the changes recently introduced where we separate the enabled/disabled promotions into 2 separate listings.