cli: only apply hot loader hook support alias for react 16

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/lucky-lemons-serve.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Switched to only apply `@hot-loader/react-dom` [Webpack aliasing](https://github.com/hot-loader/react-dom/tree/master/source#webpack) when using React 16.

.changeset/nice-lobsters-tie.md

@@ -4,7 +4,7 @@
 
 Migrated the app template to React 17.
 
-To apply this change to an existing app, make the following change to `packages/app/package.json`:
+To apply this change to an existing app, make sure you have updated to the latest version of `@backstage/cli`, and make the following change to `packages/app/package.json`:
 
 ```diff
      "history": "^5.0.0",