Allow different package specifications for Pip and Conda

[leroyvn]

Description

This commit allows different package specifications for Pip and Conda. In practice, dependencies can now be specified either this way:

main:
  packages:
    - "attrs>=22.2"

or that way:

recommended:
  packages:
    - pip: "graphviz>=0.20"
      conda: "python-graphviz>=0.20"

This allows using different package names for Pip and Conda.

Checklist

• The code follows the relevant coding guidelines
• The code generates no new warnings
• The code is appropriately documented
• The code is tested to prove its function
• The feature branch is rebased on the current state of the main branch
• I updated the change log if relevant
• I give permission that the Eradiate project may redistribute my contributions under the terms of its license

[wint3ria]

SGTM