Add support for skill layers in model manifests:
- server/skill.go: New file with skill extraction and packaging
- GetSkillsPath: Returns path to extracted skills cache
- ExtractSkillBlob: Extracts skill tar.gz to cache
- CreateSkillLayer: Creates skill blob from directory
- ParseSkillName/GetSkillManifestPath: Skill name handling
- server/images.go: Extract skill layers on pull
- server/create.go: Create skill layers from SKILL directives
- server/routes.go: Skill-related route handling
Skills are stored as gzipped tar archives with MediaType
"application/vnd.ollama.image.skill".
ParthSareen