Add cards for issues

[ravi11o]

Each board will have one or more lists like design, frontend, backend etc..
Each list can have one or more issues. For each issue, we will create a card.

Each card in the list must have

• title -> required
• slug
• due date
• members - []
• isComplete -> Boolean

Optional fields are

• description
• labels -> [string]

Add endpoints for create/update/delete cards, also add endpoints for add/remove members from cards.
Add endpoint for changing the due date as well as label for each card.