add assertions for cutout bounds, solves #158

[FabianHofmann]

Closes #158

Changes proposed in this Pull Request

See #158

It still remains to figure out whether the grid should totally include all offshore regions

• If not, the second assertion (now commented) can be deleted
• If yes, the second assertion has to be uncommented and the bounds of the cutout adjusted in the config.default.

Checklist

• I tested my contribution locally and it seems to work fine.
• Code and workflow changes are sufficiently documented.
• Newly introduced dependencies are added to environment.yaml and environment.docs.yaml.
• Changes in configuration options are added in all of config.default.yaml, config.tutorial.yaml, and test/config.test1.yaml.
• Changes in configuration options are also documented in doc/configtables/*.csv and line references are adjusted in doc/configuration.rst and doc/tutorial.rst.
• A note for the release notes doc/release_notes.rst is amended in the format of previous release notes.

[FabianHofmann]

Closing this in favour of new PR tackling #158