docs: add HTML iframe webcam service

[justinh-rahb]

• Added a new entry to the webcam services table describing the HTML Iframe service and that it embeds the configured stream_url as a webpage inside an <iframe> and supports rotation/flip.
• Documented the new Aspect ratio field with the default value 16:9, accepted formats WIDTH:HEIGHT or WIDTH/HEIGHT, and an example 16:9.
• Included a short security note advising users to only embed sources they trust since the iframe URL is user-provided.
• Changes made in overview/settings/webcams.md to add the above documentation.

If there are any changes to the verbiage or location of this you'd like, please let me know.

I also made sure to leave maintainer edits enabled this time 😅

[meteyou]

Thank you very much! Its nice to have the docs up2date!

[justinh-rahb]

Thank you very much! Its nice to have the docs up2date!

as a fellow maintainer of projects, I too appreciate when it's not forgotten, so np!