Closes #1661.

Changes proposed in this Pull Request

When one of the carrier_groups defined for plot_balance_timeseries is not included in the model scope (e.g. heating), the workflow will break at this postprocessing step since none of the carriers defined for this group are included in the network. Described in #1661.

This PR introduces a check and skip for missing/empty carrier_groups in plot_balance_timeseries.py.

Checklist

• I tested my contribution locally and it works as intended.
• Code and workflow changes are sufficiently documented.
• Changed dependencies are added to envs/environment.yaml.
• Changes in configuration options are added in config/config.default.yaml.
• Changes in configuration options are documented in doc/configtables/*.csv.
• Sources of newly added data are documented in doc/data_sources.rst.
• A release note doc/release_notes.rst is added.