[WIP] Update ADIOS2 to support Podman compatibility

[Copilot]

Podman Support for ADIOS2 XRootD Docker Build

Summary

Modified PR #4822 to support both Docker and Podman container runtimes.

Changes Made

• Auto-detection of container runtime

  • Checks for docker first, falls back to podman
  • User can override with CONTAINER_RUNTIME environment variable
  • Exits with clear error if neither is found

• Docker support (backward compatible)

  • Uses docker buildx build with --load flag
  • Maintains existing multi-platform build capability

• Podman support (new)

  • Uses podman build with --platform flag
  • No buildx required (podman supports --platform natively)
  • Compatible with podman 4.x and newer

• Documentation

  • Created comprehensive README.md
  • Documents both Docker and Podman usage
  • Includes troubleshooting guide
  • Examples for manual override

• Testing

  • Validated syntax
  • Tested auto-detection logic
  • Verified podman availability check
  • Confirmed backward compatibility

Usage Examples

Auto-detect (prefers docker):

./build.sh

Explicit podman:

CONTAINER_RUNTIME=podman ./build.sh

Explicit docker:

CONTAINER_RUNTIME=docker ./build.sh

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