[Feature]: Add the possibility to override styling variable in chrome extension

[matthieu-crouzet]

Context

Currently it is not possible to override theme variable easily

Proposal

Provide a solution in the chrome extension

• [x] Add a form to override variable flagged with the tag theme
• [x] Group variable by category / type / component
• [ ] Add a tab for theming in the component panel (display only component variable)
• [ ] Add a mechanism to validate variable value (optional)