Improve `pixi add --pypi` CLI API features for local source packages

[matthewfeickert]

trafficstars

Problem description

At the moment

$ pixi --version
pixi 0.59.0

if one wants to add a local source Python project to a Pixi manifest using the pixi add CLI API one has to do the equivalent of

pixi add --pypi "package-name @ file:///absolute/path/to/package"

which will then produce the following in the Pixi manifest

[pypi-dependencies]
package-name = { path = "/absolute/path/to/package" }

This is not portable across machines, and so the user needs to manually edit the Pixi manifest to use a relative path from the manifest location

[pypi-dependencies]
package-name = { path = "." }

It would be extremely useful if this was available from the pixi add --pypi CLI API through the equivalent of something like

pixi add --pypi "package-name @ ."

Additionally, at the moment there seems to be no way to support installing local Python packages with dependency groups. There is the ability to get dependency groups in a Pixi manifest that you control (https://pixi.sh/latest/python/pyproject_toml/#dependency-groups), but not to interact with a project that you do not control that uses them.

In a similar way that if you provide an extra to a pixi add --pypi command

pixi add --pypi "package-name[dev] @ file:///absolute/path/to/package"

Pixi adds an extras field to the manifest

[pypi-dependencies]
package-name = { path = "/absolute/path/to/package", extras = ["dev"] }

it would be useful to be able to expose a manifest option for the pypi-dependencies that also corresponds to a CLI API option that would enable something along the lines of

pixi add --pypi "package-name[dev] @ file:///absolute/path/to/package" --group test

and

[pypi-dependencies]
package-name = { path = "/absolute/path/to/package", extras = ["dev"], dependency-groups = ["test"] }