fix: lower the lower bound for power grouping years

[tgilon]

Closes #2096.

Changes proposed in this Pull Request

This PR suggests lowering the lower bound for power grouping years. This resolves the issue of existing assets that were built before 1920.

Checklist

• I tested my contribution locally and it works as intended.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to pixi.toml (using pixi add <dependency-name>).
• Changes in configuration options are added in config/config.default.yaml.
• Changes in configuration options are documented in doc/configtables/*.csv.
• For new data sources or versions, these instructions have been followed.
• A release note doc/release_notes.rst is added.