Write new basic forms article for learn

[chrisdavidmills]

Description

This PR updates the Learn web development Forms and buttons in HTML article, which is currently incomplete.

A couple of notes:

• There are a couple of links to externally hosted examples, which currently 404. I was intending to put them somewhere like the learning-area repo, but I've not put them in place yet as I wanted to get the code reviewed first.
• There is a lot of forms content not covered here, but I wanted to try to create a single article that covered enough of the basics to give the reader just enough for now. Let me know if you think there is anything critical missing.
• Also let me know if you feel like anything is superfluous or waffly. I want to make it shorter if possible ;-)

Motivation

Additional details

Related issues and pull requests

[github-actions]

Preview URLs

• /en-US/docs/Learn_web_development/Core/Structuring_content/HTML_forms

External URLs (1)

URL: /en-US/docs/Learn_web_development/Core/Structuring_content/HTML_forms
Title: Forms and buttons in HTML

• https://css-tricks.com/html-inputs-and-labels-a-love-story/ (1 time) (Note! This may be a new URL 👀)