Make project home configurable #689

[FlorianK13]

• Remove get_data_version_dir() - This function is redundant as its logic can be inlined where it's used (e.g., in mastr.py:438 as os.path.join(self.output_dir, "data", get_data_config()))
• Add MASTR_PROJECT_HOME_DIR environment variable support to get_project_home_dir() - Currently only OUTPUT_PATH is respected, but users need to be able to override the base project home directory itself (where credentials and config are stored), not just the output path - this is relevant for setting up a project home for testing

PR-Assignee

• 🐙 Follow the workflow in CONTRIBUTING.md
• 📝 Update the CHANGELOG.md
• 📙 Update the documentation

Reviewer

• 🐙 Follow the Reviewer Guidelines
• 🐙 Provided feedback and show sufficient appreciation for the work done

[FlorianK13]

Sure tests fail, but that is why we have #749