Allow customization of the search form via a plugin

Problem/Motivation

Currently, the ExternalMediaProviderInterface in the Media External module defines methods for searching and loading external media items. However, there is no provision for customizing the search form's input and output.

Steps to reproduce

Proposed resolution

Introduce a new method in the ExternalMediaProviderInterface that allows for the customization of the search form's input and output. This method would enable developers to modify the search form.

Remaining tasks

User interface changes

This change would allow for modifications to the search form's fields and layout, depending on the implementation by developers. The default user interface would remain unchanged unless customized by a plugin.

API changes

Data model changes