feat: add python PEP621/PEP5128 support

[paquiteau]

Hi there,

This PR add support for PEP621 python projects, by detecting the standardized pyproject.toml file.

I must admit that I am not confortable with the eldev test framework, and I could not find out if and how i could write a test for this new setup.

Thank you for all the work on this essential package.

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Thanks!

[bbatsov]

I must admit that I am not confortable with the eldev test framework, and I could not find out if and how i could write a test for this new setup.

No worries, we don't have much tests about the project detection anyways.

[paquiteau]

Nice,
Tell me if anything more is required before merging :)