add jest as extension devDep, go back to using makefile foreach syntax

Signed-off-by: Sebastian Malton <sebastian@malton.name>

extensions/support-page/package.json

@@ -16,6 +16,7 @@
     "@types/react-router": "^5.1.8",
     "@types/webpack": "^4.41.17",
     "css-loader": "^5.0.0",
+    "jest": "^26.6.3",
     "mobx": "^5.15.5",
     "react": "^16.13.1",
     "sass-loader": "^10.0.4",