Interesting! I think I've been missing something. I'm checking on the documentation and will probably implement this on the next renewal or possibly early; this will save me $7 for every domain.
https://caddyserver.com/docs/automatic-httpswell, i don't think you are going to be able to set this up with namecheap.
i'm pretty sure caddy doesn't work with cpanel, you could use let's encrypt plugin instead but namecheap doesn't allow installing plugins in shared hosting either.
if you want to save that $7 per domain and don't want to manage your own hosting, you can always route your domains through cloudflare and use their free SSL.