refactor: department pages

[joaodiaslobo]

This is kind of a big one, feel free to take your time to review this PR. The ultimate goal is for this to set the platforms' department features at a solid 80% 🚀

• Department index with department cards (any)
• Department show with department name, description, banner, collaborators snippet, recent activity (for now has an empty state because association logic is missing) (any)
• Department show action buttons (ask to collaborate (any), view kanban board (collaborators & admin, will be done in another PR), view collaborators table (admin), edit department details (admin)
• Change department name, description and banner (admin)
• Chose whether a department is accepting new collaborators (admin)
• View collaborators, and requests to join (admin)
• Approve or deny collaborator requests
• View collaborators (user)
• Request to join department (any)
• Ability to archive departments (admin)
• Email to all admins of an organization collaborators of a department on new collaborator request (admin)
• Email to collaborator when their request is accepted (any)

Also adds a cool gradient component that can be used for placeholder banners and such.
Also fixes some missing associations related to the user entity.

[MarioRodrigues10]

An email should be send when an user applies to be a collaborator and when it's accepted.

[MarioRodrigues10]

Awesome 🚀