[rich-text-editor] Support uploading images to server instead of embedding as bas64 encoded data

[jiezaizone]

Mode in RTE component that allows you to upload the image to the server for embedding into the rendered text, instead of embedding the image base64 encoded as part of the text data.

[web-padawan]

Thanks for the issue. This is not currently supported.

[alvarezguille]

Also related to vaadin/vaadin-rich-text-editor#86

[TatuLund]

Probably this would require integrating this plugin: https://github.com/NoelOConnell/quill-image-uploader