Allow addding more than one local DNS/CNAME record

[yubiuser]

What does this PR aim to accomplish?:

Adds the ability to add multiple local DNS records/CNAMEs via web interface (comma-separated). The code for adding multiple CNAME records was written already, but missed the last step (a loop to add them) so only one record was added.

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[DL6ER]

Seems to work fine, going ➡️ devel now