Add marketplace.json for skills

[askpt]

Is your feature request related to a problem? Please describe.
I would like to have the skills to use the new marketplace.json format.
See more information here:

• https://docs.github.com/en/copilot/how-tos/copilot-cli/customize-copilot/plugins-marketplace?versionId=free-pro-team%40latest&productId=copilot
• https://docs.gofastskill.com/registry/marketplace-json

This will allow a more efficient skill discovery in several AI tooling.