[ads] Add `Sponsored Images & Videos` option to New Tab Page setting

[aseren]

We need to update Setting > New Tab Page as follows:

“Background Image” to “Background”

Image Type from
	Default Images
	Sponsored (Currently the default)
To
	Default Images
	Sponsored Images
	Sponsored Images & Videos (Make Default)

[tmancey]

Blocked because the CRX package would need updating to include both a static image and video.

[tmancey]

Closing as out of scope, thanks

[kjozwiak]

The above requires 1.70.103 or higher for 1.70.x verification 👍