Improving code readability for lists (index.js and db_lists.js)

[rdwebdesign]

By submitting this pull request, I confirm the following:

• 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.
• I am willing to help maintain this change if there are issues with it later.
• I give this submission freely and claim no ownership.
• It is compatible with the EUPL 1.2 license
• I have squashed any insignificant commits. (git rebase)
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What does this PR aim to accomplish?:

This PR improves code readability and I think it might make maintenance easier.

How does this PR accomplish the above?:

Two new functions created to simplify the code, reducing the number of concatenations and mixed HTML tags.

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

none

[yubiuser]

I'm fine with that change but would like to get input from others as it affects how we write and style code.

[Relluem94]

looks fine

[DL6ER]

I don't really think it affects our styling much. Anything will be rewritten at some, hopefully not even that distant, point.

[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