[cypress] Percy for ember app

[PraveenAsokan]

Outcome

Include Percy command into cypress steps to do visual testing of ember app.

Scope

• [x] Install required Percy dependencies
• [x] Add the Percy snapshot command to the required step
• [ ] Run and verify the working behavior of the tests

[PraveenAsokan]

I've installed the dependencies and updated the script with the Percy snapshot command. Percy took the snapshots successfully, but there is an issue in uploading those shots to the project. I'll look into it once back.