- Added Manifest struct to encapsulate plugin metadata and installation details.
- Implemented ManifestFromRelease and ManifestFromPlugin functions for creating manifests from releases and plugins.
- Enhanced Plugin struct to include Versions and InstallPlan for direct installations.
- Introduced validation for direct install type, ensuring artifacts are correctly specified.
- Updated registry validation to support new schema version and direct install requirements.
- Added tests for parsing and validating direct install plugins, ensuring correct artifact handling.
