feat: add plugin slot for content iframe error component (#1771)

* feat: add plugin slot for content iframe error component

* style: quality

* fix: copilot suggestions

src/courseware/course/sequence/Unit/ContentIFrame.jsx

@@ -1,8 +1,8 @@
 import PropTypes from 'prop-types';
 
-import { ErrorPage } from '@edx/frontend-platform/react';
 import { ModalDialog } from '@openedx/paragon';
 import { ContentIFrameLoaderSlot } from '../../../../plugin-slots/ContentIFrameLoaderSlot';
+import { ContentIFrameErrorSlot } from '../../../../plugin-slots/ContentIFrameErrorSlot';
 
 import * as hooks from './hooks';
 
@@ -66,7 +66,11 @@ const ContentIFrame = ({
   return (
     <>
       {(shouldShowContent && !hasLoaded) && (
-        showError ? <ErrorPage /> : <ContentIFrameLoaderSlot courseId={courseId} loadingMessage={loadingMessage} />
+        showError ? (
+          <ContentIFrameErrorSlot courseId={courseId} />
+        ) : (
+          <ContentIFrameLoaderSlot courseId={courseId} loadingMessage={loadingMessage} />
+        )
       )}
       {shouldShowContent && (
         <div className="unit-iframe-wrapper">