Show admin pointer for AMP admin screen when updating to 1.0

[westonruter]

Since 1.0 introduces an admin UI for managing the theme support mode, including allowing the user to opt-in to paired and native modes without having to make any code changes, we should add an admin pointer to invite users to try out the new modes:

This could be paired with the ability to do a scan of their site to check for compatibility (see #1007).

[kienstra]

Moving To "Ready For Merging"

This might be able to use functional testing. But this is hard to test, as once you dismiss the pointer, it never appears again.

So once this is deployed to a staging environment, someone might dismiss the pointer before it can be tested.