Admin - Requests - Checkout Page

[Frama-99]

This page should give admins the ability to choose an available equipment instance for every piece of equipment requested in a given request. The form should have validation so that every piece of equipment is given an instance identifier. At the bottom, it should have a "confirm checkout" button. When this button is pressed, send a POST to the backend. The backend should do a final check for whether those instances are available for the requested times (though this should always succeed, just to double-check) and return a success message. The page should then redirect to a request summary page with a checkout successful message.

A bonus feature is to allow additional pieces of equipment to be added on checkout.