Fix set_time_series_active_power_predefined to auto-set timeindex whe…

[nader-00]

Description

Fixes an issue where [set_time_series_active_power_predefined] could leave [TimeSeries.timeindex] empty when importing predefined profiles without an explicit timeindex.

• Automatically set TimeSeries.timeindex to default year (2011 or scenario-based) when importing predefined time series without explicit timeindex
• Add warning log when auto-setting timeindex
• Add regression test to ensure timeindex is properly set

Fixes #457

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