poetry: support for poetry metadata format 2.0

[GabMus]

No description provided.

[mig5]

Thank you for this! I applied this as a patch and it has solved the problem for me when running flatpak-poetry-generator.py against my poetry.lock after I upgraded poetry to version 1.5.0.

[ENDrain]

LGTM. Maybe could also add a line in README.md listing metadata formats supported, but not sure if that's necessary. @mig5, since this worked for you could you also please add an approving review?

[GabMus]

I really think we should merge this

[d4nj1]

Would also be nice if the --yaml output format could be added similar to

https://github.com/flatpak/flatpak-builder-tools/blob/master/pip/flatpak-pip-generator#L55-L67
with
https://github.com/flatpak/flatpak-builder-tools/blob/master/pip/flatpak-pip-generator#L480-L491