allow specifying where to spawn

[KiaraGrouwstra]

we are now able to bind spawn commands to keybinds, trigger them on login, or script them thru niri msg action.
however, the current mechanics have new windows spawn in a location depending on the focus workspace and window, while one might imagine wanting to script this otherwise, e.g. to have applications spawned in a specific workspace.
it would be nice if such an option were exposed, if maybe not the highest priority. :)

[YaLTeR]

Hmm, I sense a connection to window rules here. I.e. you might want to set window rules like open-on-output (or, when it happens, open-on-workspace) for a particular spawn (or spawn-at-startup). Need to think how to best do this.

[KiaraGrouwstra]

i guess workspace number aside there is also window position within a workspace, e.g. spawn to the left of the active window there, spawn as the right-most window, spawn in position 2 from the left... i dunno what standards exist on this kinda stuff tho, if any.