Set up CNAME to cloudflare-ipfs.com when one doesn't exist

When deploying a new website using the Cloudflare DNS, `ipfs-deploy --dns cloudflare` sets the `_dnslink` TXT record, but not the CNAME.

This means that accessing the new website from an IPFS gateway (local or public) works, but going to the domain's dnslinked address directly results in a DNS error.

By default, `ipfs-deploy` opens the browser to this new dnslinked address right after pinning it and creating the `_dnslink` record, so it's confusing/jarring to get an error screen from the browser when everything actually worked fine.

One solution would be to automatically set up the CNAME record as well (if it doesn't yet exist), changing the behavior of the `--dns` flag.

If making the distinction more explicit is desired, the `--dns` flag could be deprecated (but keep working for now) and two separate flags, like `--dnslink` and `--cname` could be created, though I'm not sure the added cognitive load is worth it.