Enhance compatibility and improve Julia binary detection

[joda9]

• Updated Project.toml to support multiple Julia versions (1.6 to 1.11) and PowerModels versions (0.19.6 to 0.21).
• Added a function in powermodels_opf.py to find a suitable Julia binary, prioritizing julia1.11 and ensuring the version is >= 1.6.
• Modified the pm_optimize function to utilize the detected Julia binary when starting the Julia process.
• Introduced pytest.ini configuration file for improved testing setup.

Description

Please include a summary of the change and which issue is fixed.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• New and adjusted code is formatted using the pre-commit hooks
• New and adjusted code includes type hinting now
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• The Read the Docs documentation is compiling correctly
• If new packages are needed, I added them the setup.py, and if needed the rtd_requirements.txt, the eDisGo_env.yml and the eDisGo_env_dev.yml.
• I have added new features to the corresponding whatsnew file