Kanban bucket limits (#652)

Fix integration tests

Generate swagger docs

Add test for moving a task between buckets

Add check for bucket limit when updating a task

Add fixture to ensure a bucket with a high limit will never exceed the limit

Refactor bucket limit check into seperate function

Add test for creating and fix

Fix unexported field

Add error in case a task was added to a bucket which has its limit already exceeded

Add migration to add new task field

Add limit field to buckets

Co-authored-by: kolaente <k@knt.li>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/652

pkg/models/kanban.go

@@ -35,6 +35,9 @@ type Bucket struct {
 	// All tasks which belong to this bucket.
 	Tasks []*Task `xorm:"-" json:"tasks"`
 
+	// How many tasks can be at the same time on this board max
+	Limit int64 `xorm:"default 0" json:"limit"`
+
 	// A timestamp when this bucket was created. You cannot change this value.
 	Created time.Time `xorm:"created not null" json:"created"`
 	// A timestamp when this bucket was last updated. You cannot change this value.