Add Bundles resolver for OCI artifacts

[vdemeester]

Summary

Implements Tekton Bundles resolver to fetch tasks from OCI registries. This completes full Tekton resolver parity and provides production-ready versioned task distribution.

Features

Bundles Resolver

• Pull tasks from any OCI-compliant registry (Docker Hub, GHCR, GCR, ECR, ACR)
• Support for both tags and SHA256 digests for immutable references
• Authentication via ~/.docker/config.json (standard Docker credentials)
• Content-addressable caching
• Case-insensitive kind matching (Task vs task)

Implementation

• Uses github.com/google/go-containerregistry library (official Google library)
• Extracts Tekton YAML from OCI image layers
• Supports extracting specific resources by name from bundles
• Default kind: task (also supports pipeline)

Bundle Reference Formats

# Tag-based reference
taskRef:
  resolver: bundles
  params:
  - name: bundle
    value: gcr.io/tekton-releases/catalog/upstream/git-clone:0.9
  - name: name
    value: git-clone

# Digest-based reference (immutable)
taskRef:
  resolver: bundles
  params:
  - name: bundle
    value: gcr.io/tekton-releases/catalog/upstream/git-clone@sha256:abc123...
  - name: name
    value: git-clone

Changes

• New file: pkg/parser/bundles_resolver_test.go - Comprehensive test suite (6 tests)
• Updated: pkg/parser/resolver.go - Added resolveBundles() implementation
• New file: examples/resolvers/bundles-resolver-pipelinerun.yaml - Example usage
• Updated: examples/resolvers/README.md - Bundles documentation with auth guide
• Updated: README.md - Added bundles resolver to features list
• Dependencies: Added github.com/google/go-containerregistry@v0.20.7

Test Coverage

• 6 bundles-specific tests (all passing)
• Mock OCI registry for unit tests
• Error handling: missing params, invalid format, nonexistent registry
• Caching behavior verification
• All 60+ parser tests passing

Authentication Examples

Works with standard Docker authentication:

# Docker Hub
docker login

# GHCR (GitHub Container Registry)
echo $GITHUB_TOKEN | docker login ghcr.io -u USERNAME --password-stdin

# GCR (Google Container Registry)
gcloud auth configure-docker

# ECR (AWS Container Registry)
aws ecr get-login-password | docker login --username AWS --password-stdin $ECR_REGISTRY

Resolver Completion Status

With this PR, all four Tekton resolvers are now implemented:

Resolver	Status	Use Case
HTTP	✅ Complete	Fetch from raw URLs
Git	✅ Complete	Clone repos and extract tasks
Hub	✅ Complete	Query Artifact Hub catalogs
Bundles	✅ Complete	Pull from OCI registries

🤖 Generated with Claude Code