Plugin Directory: Add checkbox on submission page

[Ipstenu]

Add a checkbox to the submission page that requires confirmation the submitter is:

1. Submitting their own work
2. Agrees to follow the developer guidelines

It can link to ​https://developer.wordpress.org/plugins/wordpress-org/detailed-plugin-guidelines/ for edification.

Something like...

I confirm this plugin is my own, original, work, and complies to all the <a href="https://developer.wordpress.org/plugins/wordpress-org/detailed-plugin-guidelines/">Plugin Developer Guidelines</a>.

This will act, in part, as a self-protection for people who later argue they didn't agree to the guidelines.

[dd32]

After chatting with others, the wording here might open more questions from some that doesn't quite meet the intention, it might seem nitpicky, but when being overly explicit it seems worth it.

I confirm this plugin is my own, original, work

• "It's mine, but I forked JangaBlocks! It's a new work and I've given attribution, but it's not entirely my original work?"
• "I wrote this plugin, but it uses a variety of CC0 licensed works that I didn't author?"
• "Oh yes I clicked that, because it's my plugin, but I just wanted you to review it so we could get autoupdates on our site!" (okay, this is stretching it.. but..)
• "The plugin is written by others at the company.. not me? I'm just the Open Source rep!"

I went with a more generic text on the ​Themes upload page:

[] I have permission to upload this theme to WordPress.org for others to use and share.
[] The theme complies with all Theme Guidelines.
[] The theme, and all included assets, are licenced as GPL or are under a GPL compatible license.

Perhaps for consistency we can just tweak that for plugins a little?

[] I have read the <a href="​https://developer.wordpress.org/plugins/wordpress-org/plugin-developer-faq/">Frequently Asked Questions</a>.
[] This plugin complies with all <a href="​https://developer.wordpress.org/plugins/wordpress-org/detailed-plugin-guidelines/">Plugin Guidelines</a>.
[] I have permission to upload this plugin to WordPress.org for others to use and share.
[] This plugin, all included libraries, and other included assets are licenced as GPL or are under a GPL compatible license.

[Ipstenu]

I like that better than my idea :) Excellent! This is great!

[dd32]

In 11403:

Plugin Directory: Upload: Add a series of requires checkboxes to the upload screen to ensure that uploaders have read and hopefully grasp the plugin guidelines and the purpose of uploading plugins.

Fixes #5993.