Add fallback `alt` text to the images if it is not directly set by ExtensionConfig

https://thomas-mathai.neetorecord.com/watch/ac7edccd26da5fc59cee

<img width="1015" alt="Image" src="https://github.com/user-attachments/assets/49b455a7-a1e0-4fb1-af5e-af3e9f1c8742" />


@AbhayVAshokan _a