feat: Add support for private PyPI repositories

[yustme]

Summary

Adds support for private PyPI repositories (e.g., Artifactory, Nexus) in the custom Python component. Users can now configure a private PyPI repository as an additional package index alongside the public PyPI.

Configuration options added:

• enabled: Toggle to enable/disable the feature
• url: Private PyPI repository URL (PEP 503 compliant simple index)
• username: Optional username for authentication
• #password: Encrypted password/token for authentication

The implementation uses uv's environment variables (UV_INDEX, UV_INDEX_PRIVATE_USERNAME, UV_INDEX_PRIVATE_PASSWORD) to configure the additional index and authentication.

Review & Testing Checklist for Human

• Verify UV_INDEX format: Confirm that UV_INDEX=private=<url> is the correct format for uv to recognize an additional index. The uv docs suggest this should work but needs verification.
• Test with actual private PyPI: This has not been tested end-to-end with a real Artifactory/Nexus instance. Test with both authenticated and unauthenticated private repositories.
• Verify encrypted password mapping: The schema uses #password which should map to encrypted_password via the encrypted_keys function - verify this works correctly.
• Check uv sync behavior: When using Git source with pyproject.toml/uv.lock, verify that uv sync --inexact respects the UV_INDEX environment variable.

Recommended test plan:

1. Configure a test private PyPI repository (or use an existing Artifactory instance)
2. Create a component configuration with private_pypi.enabled=true and valid credentials
3. Test installing a package that only exists in the private repository
4. Verify both CODE and GIT source modes work correctly

Notes

Note: _setup_private_pypi_env is called redundantly in install_packages_for_repository (once directly, once via install_packages). This is harmless but could be cleaned up.

Link to Devin run: https://app.devin.ai/sessions/a858822356fb4c66962081b4b638ee82
Requested by: Vojta Tuma (@yustme)

Release Notes

Justification, description

Adds support for private PyPI repositories to enable users to install packages from internal package indexes like Artifactory or Nexus.

Plans for Customer Communication

N/A

Impact Analysis

Low risk - feature is opt-in and disabled by default. Existing configurations without private_pypi will continue to work unchanged.

Deployment Plan

N/A

Rollback Plan

N/A

Post-Release Support Plan

N/A

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