Add new interface listening option "bind"

[DL6ER]

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• I have read and understood the contributors guide, as well as this entire template.
• I have made only one major change in my proposed changes.
• I have commented my proposed changes within the code.
• I have tested my proposed changes, and have included unit tests where possible.
• I am willing to help maintain this change if there are issues with it later.
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• I have squashed any insignificant commits. (git rebase)

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What does this PR aim to accomplish?:

Part of the fix for pi-hole/web#2009

How does this PR accomplish the above?:

Add interpretation for new interface option bind

Accompanying pull requests:

• Improve interface settings web#2011
• Clarify interface listening behavior docs#620

What documentation changes (if any) are needed to support this PR?:

See pi-hole/docs#620

[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-v5-12-web-v5-9-and-core-v5-7-released/51795/1