gestures: Add gestures:workspace_swipe_min_fingers option (#6342)

When gestures:workspace_swipe_min_fingers is enabled,
gestures:workspace_swipe_fingers is considered to be the minimum
number of fingers required to swipe.

This behavior is more similar to sway and macOS's default behavior.

For example, this allows you to set workspace_swipe_fingers to 3,
but swipe with 4 or more fingers instead of 3.