Adds focus: false to newly created modal dialogs (#3539)

Without forcing `focus: false`, a Bootstrap modal rendered by RailsAdmin will not allow other modals to have focus for their inputs. This breaks tools like CKEditor (when adding a link within the WYSIWYG, for example, users are unable to interact with fields within the link popup).

ref: https://getbootstrap.com/docs/5.0/components/modal/#options

src/rails_admin/remote-form.js

@@ -183,6 +183,7 @@ import * as bootstrap from "bootstrap";
         new bootstrap.Modal(widget.dialog[0], {
           keyboard: true,
           backdrop: true,
+          focus: false,
           show: true,
         }).show();
       }