Context:

The new RichTextField is missing a proper way to configure font and font background colors

Follow the instructions https://ckeditor.com/docs/ckeditor5/latest/features/font.html#configuring-the-font-color-and-font-background-color-features

Dev Notes:

1. Color code format: does it support hex format?
   1. If yes, could RichTextFieldDefinition#colors be reused as the legacy RichTextField used hex format?
2. Should font and font background colors share the same config
3. Other component styling such as the table cell's color is out of this ticket's scope