Change default headless resolution to 1920x1080

[kuceb]

When users run in a headless browser, we should default to a higher resolution for useful screenshots/videos out of the box

Change default headless resolution to 1920x1080 from 1280x720.

[cypress-bot]

The code for this is done in cypress-io/cypress#15686, but has yet to be released.
We'll update this issue and reference the changelog when it's released.

[bahmutov]

Released in v7.0.0