Feature/#1446 adapt dataset gas demand to new scenarios

[cvarela-dlr]

Fixes #1446 .

Please review after PR #1519.

Key Changes

• Adapt Gas_Demand TaskGroup, mainly by modifying industrial_gas_demand.py
• A scenario-aware IndustrialGasDemand class is defined
• pipeline.py is modified accordingly
• Demand data fallbacks to 2035. ffe source is unavailable. A correct data source is still needed.
• Pending is treatment for reGon2045, with potential updates on reGon2037 parameters.

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[CarlosEpia]

Please merge dev into this branch. Then proceed to merge it into server-run-11-09 so it will be tested for the Germany case.