Add Digest Export and Manifest Creation for Multi-Arch Docker Builds

[Bcoderx6]

This pull request enhances the Docker image build workflow to support exporting image digests and creating a manifest list for multi-architecture Docker builds. The changes include:

• Digest Export: The build job now exports digests for each platform and uploads them as artifacts.
• Manifest Creation: The merge job downloads all digests and creates a manifest list with these digests for each platform.
• Simulated Image Inspection: Added steps to simulate image inspection and creation of a manifest list.

The login and logout steps for DockerHub are currently commented out. Uncomment these steps if DockerHub authentication is required. The workflow now supports linux/amd64, linux/arm64, linux/arm/v6, and linux/arm/v7 platforms.