Fix all warnings in RTD builds #342
Description
What needs to get done
RTD builds have warnings that are currently being ignored:
/home/docs/checkouts/readthedocs.org/user_builds/canonical-craft-cli/checkouts/340/craft_cli/helptexts.py:docstring of craft_cli.helptexts.HelpBuilder:1: WARNING: more than one target found for cross-reference 'CommandGroup': craft_cli.CommandGroup, craft_cli.dispatcher.CommandGroup
/home/docs/checkouts/readthedocs.org/user_builds/canonical-craft-cli/checkouts/340/craft_cli/helptexts.py:docstring of craft_cli.helptexts.HelpBuilder.get_command_help:1: WARNING: more than one target found for cross-reference 'BaseCommand': craft_cli.BaseCommand, craft_cli.dispatcher.BaseCommand
Why it needs to get done
For better maintainability and predictability of docs builds