Add architecture-specific build parameter overrides to multiarch workflow

[Copilot]

The multiarch workflow forced identical Dockerfile/context/build_args for both ARM and AMD builds. This prevents architecture-specific optimizations like different base images, compiler flags, or build contexts.

Changes

New optional inputs with fallback logic:

• arm_dockerfile_path, arm_context, arm_build_args - ARM-specific overrides
• amd_dockerfile_path, amd_context, amd_build_args - AMD-specific overrides

Implementation:

dockerfile_path: ${{ inputs.arm_dockerfile_path != '' && inputs.arm_dockerfile_path || inputs.dockerfile_path }}

Each architecture-specific parameter falls back to the common parameter when empty, maintaining backward compatibility.

Documentation:

• Added architecture-specific inputs section with parameter table
• Example demonstrating different Dockerfiles per architecture

Usage

jobs:
  build-multiarch:
    uses: ./.github/workflows/build-multiarch-image.yml@main
    with:
      image_name: myorg/myapp
      # ARM builds with NEON optimizations
      arm_dockerfile_path: ./Dockerfile.arm64
      arm_build_args: OPTIMIZATION=neon
      # AMD builds with AVX2 optimizations  
      amd_dockerfile_path: ./Dockerfile.amd64
      amd_build_args: OPTIMIZATION=avx2
      push: true

Existing workflows continue working without modification.

Original prompt

I would like to generate a repository with reusable github action workflows - "build ARM image", "build AMD" image", "build mulitarch image" placeholder actions will work, as well as a README.md that explains how to use the actions in a workflow

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