Add poetry for dependency management and packaging

[crdanielbusch]

Description

• Add Poetry for dependency management and packaging -> add all dependencies in pyproject.toml
• Adjust action.yaml and ci.yaml to Poetry
• Check that Poetry builds openmethane_prior package in GitHub workflow
• Check that Poetry installs openmethane_prior package in GitHub workflow

Small changes unrelated to Poetry:

• Switch to environment variables for CDS API authentication
• Update commands to run the script in Readme
• Update list of authors in pyproject.toml
• snake case module names and remove om prefix (low priority, will be done in another pull request)

Checklist

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)

Notes

[lewisjared]

One other thing, can you add a target into the Makefile to build the venv? It should be in an existing copier templated project