IBX-2961: Fixed extensibility point for adding plugins in CKEditor

[dew326]

Question	Answer
JIRA issue	IBX-2961
Requires	ibexa/core#120
Type	bug
Target Ibexa version	v4.1+
BC breaks	no
Tests	Passing CI build with ibexa/core dependency Run regression for IBX-2961 commerce#102

Related changes:

• IBX-2961: Refactored Extension to rely on Encore Configuration Dumper admin-ui#471

Doc

See also ibexa/admin-ui#471 for Doc.

We need to extend this part of the documentation: https://doc.ibexa.co/en/latest/extending/extending_online_editor/#add-ckeditor-plugins

It is still needed to add plugin into the extraPlugins array, but it has to be done in a specific way.
The JS cannot be added by the default configManager or added in any encore entry. It has to be added to the ibexa-richtext-onlineeditor-js entry.

So we introduced the new configManager which will handle adding JS to the CKEditor config.
The file that must be created is ibexa.richtext.config.manager.js either in the top level project folder encore or in a Resources/encore/ folder in the bundle

the code for ibexa.richtext.config.manager.js:

const path = require('path');

module.exports = (ibexaConfig, ibexaConfigManager) => {
    ibexaConfigManager.add({
        ibexaConfig,
        entryName: 'ibexa-richtext-onlineeditor-js',
        newItems: ["path_to_file"],
    });
};

TODO:

• Ask for Code Review.