Extend AddItemToToolbar config action to provide plugin settings

Problem/Motivation

The only way currently to add editor plugin settings is to use simpleConfigUpdate which is a common hack, but technically it is a config entity, not simple config.

Steps to reproduce

See hacky recipes like this:

config:
  actions:
    editor.editor.full_html:
      simpleConfigUpdate:
        settings.plugins.ai_ckeditor_ai.dialog.autoresize: 'min-width: 600px'
        settings.plugins.ai_ckeditor_ai.dialog.height: '750'
        settings.plugins.ai_ckeditor_ai.dialog.width: '900'
        settings.plugins.ai_ckeditor_ai.dialog.dialog_class: ai-ckeditor-modal
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_completion.provider: openai__gpt-4o
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_completion.enabled: true
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_help.enabled: false
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_summarize.provider: openai__gpt-4o
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_summarize.enabled: true
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_tone.autocreate: false
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_tone.provider: openai__gpt-4o
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_tone.tone_vocabulary: ai_tones
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_tone.use_description: 1
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_tone.enabled: true
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_translate.autocreate: true
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_translate.provider: openai__gpt-4o
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_translate.translate_vocabulary: ai_languages
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_translate.use_description: false
        settings.plugins.ai_ckeditor_ai.plugins.ai_ckeditor_translate.enabled: true

Proposed resolution

Extend AddItemToToolbar config action to provide plugin settings

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet