possibility to add prefixe to relative URL

[fab2713]

Hey @panphora,

It could be nice to have a way to add a prefixe to relative URL, because the document being edited does not necessarily have the same path/domain/… as the final published page and in this case the link would be broken in this editor.

This could be configured with a new component option named relativeUrlPrefixe for example, and the end of sanitizeUrl function could be modified like:

if (hasSafeProtocol) {
  return url;
} else if (isRelative) {
  return (this.relativeUrlPrefixe || "") + url;
} else {
  return "#";
}

Thanks in advance.