Improve repository and registry parameterization

[chaptersix]

Summary

Makes Docker image publishing fully configurable while maintaining backward compatibility with both temporalio (Docker Hub) and forks (GHCR).

Changes

New Workflow Inputs (all optional with smart defaults)

• registry: Container registry (docker.io, ghcr.io, etc.)
• registry_namespace: Organization/user (defaults to repository_owner)
• image_name: Image name (defaults to "temporal")

Key Improvements

1. Smart auto-detection:

   • temporalio/cli → docker.io/temporalio/temporal
   • Forks → ghcr.io/{owner}/temporal

2. Conditional authentication:

   • GHCR: Uses GITHUB_TOKEN
   • Docker Hub: Uses DOCKER_USERNAME/DOCKER_PASSWORD secrets

3. Standardized image naming:

   • All repos now use temporal as the image name (no more temporal-cli for forks)

4. Proper Docker Hub handling:

   • Correctly handles Docker Hub's no-registry-prefix format
   • Tags: temporalio/temporal:v1.2.3 (not docker.io/temporalio/temporal:v1.2.3)

Default Behavior

For temporalio/cli (upstream):

• Registry: docker.io (auto-detected)
• Namespace: temporalio
• Image: temporal
• Result: temporalio/temporal:v1.2.3

For chaptersix/temporal-cli (fork):

• Registry: ghcr.io (auto-detected)
• Namespace: chaptersix
• Image: temporal
• Result: ghcr.io/chaptersix/temporal:v1.2.3

Benefits

• ✅ Zero configuration needed for standard use cases
• ✅ Fully configurable for custom registries
• ✅ Backward compatible with temporalio's existing setup
• ✅ Works out-of-the-box for all forks
• ✅ Ready to PR back to upstream

Testing

After merging, create a new release to verify images publish correctly to ghcr.io/chaptersix/temporal.