Fix/issue 30 sector config

[omari91]

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Changes proposed in this Pull Request

• Fixes Issue Configurations of sectorparameter get overwritten #30 (Configurations of sector parameter get overwritten): Changed the initialisation logic in scripts/pypsa-de/build_scenarios.py to use not in membership tests instead of .get(...) truthiness checks for the sector, industry, and solving config dictionaries. This prevents custom configurations from being completely overwritten and erased when the user passes an empty dictionary or False.

Checklist

Required:

• Changes are tested locally and behave as expected.
• Code and workflow changes are documented.
• A brief description of the changes has been added to Changelog.md. (Please add if needed!)

If applicable:

• Changes in configuration options are reflected in scripts/lib/validation. (N/A)
• For new data sources or versions, these instructions have been followed. (N/A)
• New rules are documented in the appropriate doc/*.rst files. (N/A)