Migrate to toml package format

[DavidStirling]

This PR updates omero-user-token to use the pyproject.toml package format.

Key changes:

• Migrated setup.py to pyproject.toml for package spec
• Reworked build system to use python -m build instead of the deprecated python setup.py install command
• Versioning migrated to setuptools-scm in keeping with other tooling
• Added an alias to the cli so that omero-user-token now works, not just omero_user_token.
• Rolled dev dependencies into the main project file as the dev group
• Final wheel construction and upload now happens with the lowest Python version, rather than the newest available

I've largely kept the build system the same, though since we have a shared wheel between all platforms/versions testing the entire python version matrix might be overkill.

[DavidStirling]

Nice catch, thanks @sbesson

[sbesson]

omero@search-test:~$ omero-user-token get
ERROR: Token for localhost is invalid!
omero@search-test:~$ omero-user-token set -u root
Password: 
Successfully set token: e081e909-bca0-4b84-bbbc-38e0c793b255@localhost:4064
omero@search-test:~$ omero-user-token get
e081e909-bca0-4b84-bbbc-38e0c793b255@localhost:4064

Looks good thanks, proposing to go ahead and tag 0.4.0 tomorrow morning to test the release workflow.

Reading the README, 2 thoughts:

• we might need to update Python 3.6+ to 3.9+ (forgotten in Require Python 3.9 as the minimum version #12 )
• is omero-user-token or omero_user_token the preferred form for the command-line utility?

[DavidStirling]

Thanks @sbesson, I've updated the readme.

While both are supported, I think we should prefer omero-user-token over the underscored version as this is more consistent with our other tooling. Nonetheless both will work in this version.