use mamba for release ci/cd on pypi pipeline

[wsavran]

this is a 2 parter:

1. we should use mamba for the publish-pypi.yml pipeline
2. we need to update the documentation to reflect that users will need to manually install the documentation packages. the best way to do this is probably to create a requirements_docs.yml and let them know they need to use that to install the sphinx dependencies.

[pabloitu]

• The publish-pypi.yml pipeline is already updated with mamba. Was the latest release automatically published in pypi using mamba @fabiolsilva , @pjmaechling?

• @wsavran I believe you already wrote in the contribution instructions (https://github.com/SCECcode/pycsep/blob/main/CONTRIBUTING.md#developer-installation) to install pycsep with pip install -e .[all]. That should install all the docs dependencies, which are specified in pycsep setup.py. Will make an update in the docs, where that is missing.