install only given dev dependency

[finswimmer]

This PR introduce a new option --dev for the poetry install command. Instead of installing all development dependencies, one can use this option, to limit the installation to the given dev dependencies. --dev can be used together with --dev-only to decide, whether the dev dependencies should be installed together with the package or without.

Closes: #3570

Pull Request Check List

• Added tests for changed code.
• Updated documentation for changed code.

[sdispater]

I think it would be better to wait for the implementation of the dependency groups before we go this route.

Poetry was never about installing single dependencies separately but always about managing groups of dependencies consistently.

Also, it could lead to option bloat and confusion which defeats the simplicity purpose of Poetry.

[jcmdln]

I think rather than providing yet another option, it would be better for poetry install to accept arguments much like how poetry add works, but only refers to packages defined in poetry.lock if it exists. Alternatively, poetry add could add some invariant option to --lock where it only adds a package based on a lockfile.

Dependency groups look nice but are overkill for parallelized jobs where you want to run one utility, like mypy, without having to install a bunch of other dependencies. The solution to that with dependency groups would be to assign something to multiple groups, one with the package name and another in a broader ci group or something if desired, but I'd rather have one less explicit location to declare since my tests are wrapped with tox anyway.

[finswimmer]

Closing this in favor of dependency-groups #4260

[github-actions]

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