Limits on columns

Is your feature request related to a problem? Please describe.
Deck is often advertised as a kanban style board, althgough it can be used in many more use cases.

One of the fundamental principles of kanban is the limits of tickets per column, that goes along with flow visualisation, as it helps the team manage and regulate the flow avoiding bottlenecks. Sometimes it is called "WIP limit" (Work In Progress).

Describe the solution you'd like
Option on each column, that can be accessed via the meatballs menu ("..." or horizontal three dots):

• No limit
• Soft limit (visual and textual alert, for example "Limit reached" in red)
• Hard limit (prevent card creation, suggest to create the card in the previous column if limit not reached yet)

Describe alternatives you've considered
Manually write a soft limit in plain text, in the column title, or as a first card (that would be differenciated and unmovable by agreement of team members).

A visual example

• Soft limit in the column title: "Stuff in flow [limit: 4]"
• Soft limit in the first card: "Limit: 4 cards"

Start by reviewing the column meatballs menu and the card-creation flow described in the issue. Determine how column limits, soft-limit alerts, hard-limit blocking, and the previous-column suggestion should behave, then verify the behavior for each limit mode.