[DX] Fix coding standards around docblocks in `settings.php`

[klonos]

There's some inconsistencies and things like missing periods/punctuation. We should fix that according to https://docs.backdropcms.org/doc-standards#general

Specifically these rules:

• All summaries (first lines of docblocks) must be under 80 characters, start with a capital letter, and end with a period (.). ...
• Sentences should be separated by single spaces.
• Comments and variable names should be in English, and use US English spelling (e.g., "color" not "colour").
• ...

[quicksketch]

Overall looks good but there are two strange situations created by separating the first sentence in each docblock. I posted some suggestions to https://github.com/backdrop/backdrop/pull/4794#pullrequestreview-2258300190.

[quicksketch]

@avpaderno Also left a round of review on the PR.