Add documentation for ena_maps modules

### Overview

Currently, the ena_maps modules have not been included in documentation build. This ticket is to add them and address any build issues associated with the addition.

Once that is done, the `RectangularSkyMap` entry in the nitpick_ignore_regex list should be deleted. See: imap_processing/docs/source/conf.py

### Related documents or information sources

_No response_