Remove "use your own certificate" phrasing from DNS-01 section

[Punitramyadav]

In the DNS-01 section of the preparation guide, there's a line that reads:

This challenge type does not require your SCIM bridge to be accessible by Let's Encrypt, and allows you to use your own certificate and/or more strictly constrain your firewall if preferred or required.

This is a bit misleading. DNS-01 is just a different validation method used by Let's Encrypt, the certificate is still issued by Let’s Encrypt. So, the mention of “allows you to use your own certificate” suggests that DNS-01 enables bring-your-own-cert functionality, which isn’t true and could confuse users.

Requesting that we remove or reword that phrase to avoid misinterpretation.