Add Docker-based workflow setup, environment fixes, and improved .gitignore

[Sarbani-Roy]

This merge request introduces a complete setup for running the NFDI4IngModelValidationPlatform on macOS via Docker, including fixes for architecture-related issues and updates to workflow configuration.

Key changes

• Added Dockerfile and configuration to run Kratos Multiphysics and FEniCS under linux/amd64 emulation on Apple Silicon.
• Pre-created Conda environments (Kratos, FEniCS, mesh, postprocessing) to resolve Snakemake failures caused by architecture mismatches in auto-created environments.
• Updated Snakemake rules to use the manually pre-built environments.
• Limited FEniCS to a single thread to avoid OpenMP/QEMU issues under emulation.
• Improved .gitignore to exclude local macOS files (.DS_Store), Python cache directories (pycache), and various benchmark-generated artifacts such as: element_size_vs_stress.pdf, metadata4ing_provenance.zip, workflow_config.json, metadata4ing_provenance, snakemake_results.

Why this is needed

• macOS cannot run Kratos natively, making Docker the only consistent cross-platform solution.
• Snakemake’s automatic conda creation fails under Apple Silicon + Docker emulation, so manually pre-created environments are necessary.
• Generated files should not pollute Git history; the updated .gitignore ensures a clean repository.

[joergfunger]

Thanks for the update, let's discuss the details today in the meeting. But I would say adding the complete DUMUX source code to this repo here is not optimal. In addition, docker is not allowed in our environments (it requires root access) as such an alternative would be to use singularity. I would also suggest to generally make an issue first before doing complex implementation changes.