Surface AMP mode types to improve Error Validation workflow

[postphotos]

As a user, I should know which mode I'm on in the error listings and whether actions I take will affect the pages on my slte.

Considered as a sub-task to #1006.

Formal ACs to come.

cc: @jwold

[jwold]

[westonruter]

This is implemented, no?

In paired mode with auto-sanitization I see:

In paired mode without auto-sanitization I see:

In native mode I see:

[kienstra]

Good point, @westonruter. #1676 implements this. Thanks for moving this into the v1.0 milestone.