Suppress empty lines during teleporter import

[yubiuser]

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• I have made only one major change in my proposed changes.
• I have commented my proposed changes within the code.
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What does this PR aim to accomplish?:

During Teleporter import deleteAllCustomDNSEntries, addCustomDNSEntry, deleteAllCustomCNAMEEntries and addCustomCNAMEEntry are called. They all finish by calling

https://github.com/pi-hole/AdminLTE/blob/5588be9c9086ec120cd3bd4dc36bc9d4ed0acd77/scripts/pi-hole/php/func.php#L432

which outputs <br> if $json is not true (which it never is during teleporter import)

https://github.com/pi-hole/AdminLTE/blob/5588be9c9086ec120cd3bd4dc36bc9d4ed0acd77/scripts/pi-hole/php/func.php#L459-L467

So for every entry in Local DNS records or CNAME Records an empty line is printed.

This PR does suppress the output by using output_buffer.

Before

After

[PromoFaux]

Please fix conflicts

[yubiuser]

Done.

[pralor-bot]

This pull request has been mentioned on Pi-hole Userspace. There might be relevant details there:

https://discourse.pi-hole.net/t/pi-hole-ftl-v5-11-web-v5-8-and-core-v5-6-released/50566/1