Update configuring-dns.md for mDNS note

[ybizeul]

[Title: describe the change in one sentence]

Add a note regarding conflicting .local domain with Multicast DNS

How to use

An extensive test is to setup a DNS server for .local domain and try to resolve a server name.
When resolve is used before dns, any request to those names will fail.

This note explains the problem and provides a workaround

Testing done

No testing done except running web site locally to check formatting.

[Describe the testing you have done before submitting this PR. Please include both the commands you issued as well as the output you got.]

• Changelog entries added in the respective changelog/ directory (user-facing change, bug fix, security fix, update)
• Inspected CI output for image differences: /boot and /usr size, packages, list files for any missing binaries, kernel modules, config files, kernel modules, etc.

[tormath1]

Thanks, can you squash your commits before merging?

[ybizeul]

Thanks, can you squash your commits before merging?

I think I managed to do it without breaking anything !