Add a "Copied to clipboard" message after clicking on copy in the show key activity

User story

As a user I want to be sure I copied the key I was just viewing after clicking on the copy button.

This issue demands that a message is displayed to the user verifying that they successfully copied the key they were just watching.

This issue is needed for the project because it improves UX, giving them confidence they copied the key correctly.

This feature can be added by adding a non-interupting popup with the text "Copied to clipboard"

Ready

This task can be considered done when

[ ] A popup is added which is displayed after clicking on the copy button in the activity displaying a key.

None