MM-62060/MM-62276 Remove video from onboarding checklist and turn iframe-has-title ESLint rule to error (#29634)

* MM-62276 Remove video from onboarding checklist

* MM-62060 Turn jsx-a11y/iframe-has-title ESLint rule to an error

webapp/platform/eslint-plugin/configs/.eslintrc-react.json

@@ -26,7 +26,7 @@
     "jsx-a11y/click-events-have-key-events": "warn",
     "jsx-a11y/heading-has-content": "error",
     "jsx-a11y/html-has-lang": "error",
-    "jsx-a11y/iframe-has-title": "warn",
+    "jsx-a11y/iframe-has-title": "error",
     "jsx-a11y/img-redundant-alt": "warn",
     "jsx-a11y/interactive-supports-focus": "warn",
     "jsx-a11y/label-has-associated-control": "error",