Add httponly = true to persistent login cookie

[PromoFaux]

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

Sets the httponly property of the persistentlogin cookie to true, discussed : #1447

[PromoFaux]

Before:

After:

[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-v5-9-web-v5-6-and-core-v5-4-released/49544/1