Add an option for submitting a screenshot when reporting webcompat issues

[ShivanKaul]

It would be extremely helpful if the user could take a screenshot when reporting webcompat issues.

There would be a button on the Report Site form that on clicking would attach and send what the page currently looks like (below browser chrome without the Report Site overlay).

[stephendonner]

Verified PASSED using

Brave | 1.65.80 Chromium: 123.0.6312.29 (Official Build) nightly (64-bit)
-- | --
Revision | cd0c2b9c6f07e8f01724294c8d7e37393a8c3a38
OS | Windows 10 Version 22H2 (Build 19045.4170)

Steps:

1. installed 1.65.80
2. launched Brave
3. loaded vox.com
4. chose Help > Report a broken site
5. filled out the form, checked the Include screenshot checkbox
6. previewed the screenshot
7. submitted the form
8. repeated the above steps, without attaching a screenshot

With screenshot

example	screenshot preview	feedback submitted

Without screenshot

example	feedback submitted

[stephendonner]

@DJAndries hello! I'd like to be able to verify my above submissions; do you know where I can find them? (In particular, the submission with the screenshot, to be sure it was sent to the server.)

[DJAndries]

@DJAndries hello! I'd like to be able to verify my above submissions; do you know where I can find them? (In particular, the submission with the screenshot, to be sure it was sent to the server.)

will DM

[stephendonner]

Confirmed via our internal metrics/feedback system that the screenshot was indeed attached:

example	example	example