Implement AJAX reload of Content blocks

Problem/Motivation

Now the content blocks use the submit action and reload the full page, which works pretty slowly.

Proposed resolution

It would be great to implement AJAX reload of all related blocks of the configured "product_list_index" on the submit event of one of the product list modifier blocks (Search, Filters, Order).

Would be good to implement a universal way to trigger the re-rendering of the blocks from the backend by a subscribed JS event. You can take a look at the BigPipe module implementation as an example.

And, together with this, get rid of the legacy /ajax/[catalog-url] endpoint.