Update publishing for poetry

[ElliottKasoar]

Resolves #17

Set up similarly to poetry-core

There's a couple of extra things we could consider doing with versions:

• Automatically update the version in __init__.py based on the tag: see https://github.com/PSDI-Biomolecular-team/aiida-gromacs/blob/master/.github/workflows/publish-on-pypi.yml#L31
• Check all the versions match e.g. the version in the toml (we can get this from poetry) == the version in __init__.py == the tag version