Package signing

Work in Progress

This part of the ecosystem is not fully standardized yet.

Some preliminary information can be found at:

• https://www.anaconda.com/blog/conda-signature-verification
• https://github.com/conda/conda-content-trust
• https://www.anaconda.com/docs/psm/cloud/user/packages#package-signatures
• https://www.anaconda.com/docs/psm/cloud/user/packages#conda-package-signature-verification
• Attestation (https://github.com/conda/ceps/blob/main/cep-0027.md)