DOC-3267: Deprecate content_css_cors option

Author: michalnieruchalski-tiugo

modules/ROOT/partials/configuration/content_css_cors.adoc

@@ -1,6 +1,8 @@
 [[content_css_cors]]
 == `+content_css_cors+`
 
+IMPORTANT: This option has been marked as *deprecated*. It will be completely removed in the upcoming {productname} 9.0 release. As an alternative, we recommend using xref:tinymce-and-cors.adoc#crossorigin[`crossorigin`] instead.
+
 When `+content_css_cors+` is set to `+true+`, the editor will add a `+crossorigin="anonymous"+` attribute to the link tags that the StyleSheetLoader uses when loading the `+content_css+`. This allows you to host the `+content_css+` on a different server than the editor itself.
 
 *Type:* `+Boolean+`