Proposal: use new style of poetry dependency declarations

[dbatten5]

As of poetry version 1.something the new way to declare dependencies is in groups, see here. This also makes it easier to install just the relevant dependencies in github actions etc. Could this cookiecutter be updated to be in line with these rcommendations?

[joelb123]

I strongly second this. It's ugly having to put module test dependencies when we could simply do installs with my module[test]. This would also make CI installs cleaner and more reflective of what a user would see.