Add DuckDNS instructions to the remote ide docs

What does this MR do and why?

A user pointed out that access to DNS records for a domain may prove to be a barrier for adoption for the Connect a remote machine to the web ide capability that our Remote Development team is building with vscode-web.

We make mention of wildcard A record services like nip.io on other docs pages (eg. https://docs.gitlab.com/charts/development/kind/), so it feels germane to do so here as well, as another means of a fast A record.

UPDATE: nip.io isn't practical (without http-01 setup, which is involved, and also potentially non-viable due to letsencrypt rate limiting) to use with certbot/letsencrypt. I've changed this MR to suggest the use of a free DDNS service such as DuckDNS. At some point, we're pointing folks to a lot of free/best-effort-only services, and it would be better to contemplate alternative technical solutions that avoid the need for a domain name.

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