Improvements and addition of functionality to the opencard

1. In the categories of PIANO and ROYALTY there will be separate models of goods for which it is necessary to implement. Conditions under which goods from these two categories will fall under the implementation of the function:
now in the admin panel there is already a filter on the availability of goods. The product can be "In stock" and "Pre-order", so the goods are filtered for issuance. Some models of pianos and grand pianos, which under the "Pre-order" the client can also order. Which ones - we decide. Therefore, we need to create a separate filter for all products in the admin "Available for direct purchase" - and options: YES or NO. If NOT - the button "ADD TO CART" on this product is changed to "PRE-ORDER". By default, after the implementation of the function and testing - to make for all products PIANO and ROYALTY - NO. We will then set the DA for the necessary ones and will change for each product separately.
The cost does not need to be removed anywhere.
2. We implement the function for all products of categories: music lessons, additional systems, piano and grand piano settings, piano and grand piano rental.