Add Ko build backend for optimized Go application builds

[kingdonb]

Goal: Add Ko as a build backend for superior Go application builds

Background:
Ko provides optimized Go application container builds without requiring Dockerfiles. It's "far and away superior in the niche it serves, at a lower price" - faster builds, smaller images, better security scanning.

Technical Requirements:

Build Configuration:

# build-config.yaml  
build_backend: ko
ko_config:
  import_path: ./cmd/myapp
  base_image: distroless.dev/static-debian12
  platforms:
    - linux/amd64  
    - linux/arm64
  env:
    - CGO_ENABLED=0
additional_tags:
  - latest
  - v1.0.0

Pipeline Integration:

• Ko build stage: ko build equivalent to Kaniko execution
• Multi-arch builds: Native Ko multi-platform support
• Registry push: Direct push to registries without intermediate files
• Manifest creation: Multi-arch manifests from Ko builds

Ko-Specific Features:

• Auto-detection: Recognize Go modules and suggest Ko backend
• Base image selection: Support for distroless, Alpine, etc.
• Build optimization: Leverage Ko's build caching and optimization
• Security scanning: Integration with Ko's vulnerability detection

Performance Benefits:

• Faster builds: No Dockerfile parsing, direct Go compilation
• Smaller images: Optimized Go binary containers
• Better caching: Ko's native build cache integration

Success Criteria:

• Can build Go applications faster than Kaniko equivalents
• Multi-architecture support maintained
• Registry compatibility with existing pipeline
• Clear performance benchmarks vs Kaniko builds

Migration Path:
Existing Go projects can opt-in to Ko builds by changing build_backend: ko in build-config.yaml without other changes.

References:

• Ko documentation: https://ko.build/
• Ko vs Docker comparison: https://ko.build/get-started/

Priority: Medium-High (immediate value for Go applications)