feat: Install main dependency group only by default

[radoshi]

• feat: Install main dependency group only by default
• fix: resolving PR comments

Summary

This PR is linked to https://github.com/paketo-buildpacks/poetry-install/pull/182 which in turn solves https://github.com/paketo-buildpacks/poetry-install/issues/180

• Breaking change : default behavior is now to install only main dependency group from pyproject.toml
• Previous behavior: poetry installs every dependencies, even the ones not necessary for production, regardless of the dependency groups
• Possibility to specify additional dependency groups with env variable BP_POETRY_INSTALL_WITH, mirroring the --with option from poetry install command README.md is updated to describe this new behaviors
• Unit and integration tests where added

Use Cases

Check https://github.com/paketo-buildpacks/poetry-install/issues/180 discussion for more details

Checklist

• [x] I have viewed, signed, and submitted the Contributor License Agreement.
• [x] I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• [x] I have added an integration test, if necessary.
• [x] I have reviewed the styleguide for guidance on my code quality.
• [x] I'm happy with the commit history on this PR (I have rebased/squashed as needed).

[linux-foundation-easycla[bot]]

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