In System Settings > Window Management > Window Behavior > Window Actions > Inner Window, Titlebar, and Frame Actions, add options to choose an action when double-clicking (left, right or middle) a window with the chosen modifier.

An example usage is to maximize a window when meta+left-double-click'ed.

Also add an action for Axis Maximization, that is, the window is maximized along the axis the cursor was in on the window, i.e. activating it on the right side of the window would maximize it horizontally only.