Add cli action to change the page width and height of the current window

Hi! I need to be able to change the width and height of the page of the currently open window programatically, at the moment there are two ways that I know to do this, both involve change the file manually and then one is to use gdbus "file-revert" and the other is to just close the program and open it again. It'd be nice being able to set that from the cli.

This is also doable thanks to this pull request: (Allow execute commands to the current desktop) inkscape!4987 (merged)