The plugin doesn’t support any assets

Problem/Motivation

The plugin inserts only HTML into Gotenberg, so the solution will ignore any images on the page or fonts, as they should be passed as additional assets.

Proposed resolution

We actually have two ways to solve the issue:

Collect all necessary information for Gotenberg and pass it as assets.
Provide a second method for page printing with a simpler implementation: optimize HTML loading within the plugin so that, ideally, we skip loading content into the $this->html property and print the page through the Gotenberg url() method.

The first way is much more problematic to implement, but it will work more as expected for other users who already work with entity_print.