[doc improvment] inconsistent usage of img_key and img_res_key in code base

I encountered a problem today using sq.pl.spatial_scatter, I have to use lowres image in my object, so I see the docstring said - Use ``img_key`` to display the image in the background.
https://github.com/scverse/squidpy/blob/e6b5b0ccd2739aa50b55c7628e685a6750249d8f/src/squidpy/pl/_spatial.py#L392
but when I specified img_key in sq.pl.spatial_scatter, I encountered error saying that it is not a valid parameter.
So I looked into the source code, and found sq.pl.spatial_scatter calls _spatial_plot
https://github.com/scverse/squidpy/blob/e6b5b0ccd2739aa50b55c7628e685a6750249d8f/src/squidpy/pl/_spatial.py#L47

in which the real parameter is named img_res_key
https://github.com/scverse/squidpy/blob/e6b5b0ccd2739aa50b55c7628e685a6750249d8f/src/squidpy/pl/_spatial.py#L57
but the docstring of _spatial_plot says img_key as well
https://github.com/scverse/squidpy/blob/e6b5b0ccd2739aa50b55c7628e685a6750249d8f/src/squidpy/pl/_spatial.py#L143

I wanted to submit a pr because this seems a simple fix, just fix the docstring would be good, but when I grep the code base I found

There seem to be a major name inconsistency, and I don't know what is the intended name in opinion of your team, so I gave up and file an issue.

Start by reading src/squidpy/pl/_spatial.py, especially the spatial_scatter entry point, _spatial_plot, and their docstrings. Trace the related img_key and img_res_key references across the codebase and confirm the intended name with maintainers. Done means the parameter and documentation references use one agreed name consistently.