Register ThemedImage component globally

so we can use different images for light and dark mode,
see https://docusaurus.io/docs/2.3.1/markdown-features/assets#themed-images

Author: pwizla

docusaurus/src/theme/MDXComponents.js

@@ -17,6 +17,7 @@ import ColumnRight from '../components/ColumnRight';
 import FeedbackPlaceholder from '../components/FeedbackPlaceholder';
 import CustomDocCard from '../components/CustomDocCard';
 import { AlphaBadge, BetaBadge, EnterpriseBadge } from '../components/Badge';
+import ThemedImage from '@theme/ThemedImage';
 
 export default {
   // Re-use the default mapping
@@ -42,4 +43,5 @@ export default {
   ColumnRight,
   FeedbackPlaceholder,
   CustomDocCard,
+  ThemedImage,
 };