Add a percy snapshot for the expanded mobile menu

[mansona]

We curren't don't have any percy snapshots for the expanded percy menu. I'm not entirely sure if we can have a percy snapshot for just one particular size 🤔 but it would be nice if it were possible.

[jenweber]

Yes, you can do size changes for individual snapshots!

https://docs.percy.io/docs/cli-configuration#per-snapshot-configuration

https://docs.percy.io/docs/ember

[DeRaowl]

Hey Manson, Would love to work on this issue?

[MinThaMie]

This is more complicated than it looks, because we need to also press the button to see what is in the menu and not only resize the Percy screenshots. I've not yet figured out how to resize the window, press the button and then take the screenshot