Frontend: Add optional description field for Project and Group CI variables

Proposal

It can be easy to forget the value and source of specific variables added to Project or Group CI variables. Occasionally we will look at our docs and see a key like GITLAB_TOKEN which relies on individual's memory to track rotations and the fields importance.

Could we include an optional description field that can be filled with arbitrary value to better describe a key's purpose?

Mockup

• Design tab
• 🔗 Figma spec