Fix Docs Build Warnings

[trevorb1]

Closes #263

Changes proposed in this Pull Request

Fixes build warnings on duplicate label reference names. Module doc strings should now be displayed on the documentation site.

Checklist

• [x] I tested my contribution locally and it seems to work fine.
• [x] Code and workflow changes are sufficiently documented.
• [x] Changed dependencies are added to envs/environment.yaml.
• [x] Changes in configuration options are added in all of config.default.yaml.
• [x] Changes in configuration options are also documented in doc/configtables/*.csv.

[ktehranchi]

hmm was this supposed to fix the docstrings not building? https://pypsa-usa.readthedocs.io/en/latest/rules-build-network.html

[trevorb1]

oh werid. Good catch @ktehranchi. It built fine on my local machine. Il re-open the issue, but keep this PR merged, as it still addressed docs warnings. Thanks!

[trevorb1]

Fixed in PR #266