Restricting network topology to interconnectors only

[toniseibold]

closes #138

create_network_topology is slightly adjusted and excludes DC links that have a underwaterfraction smaller than 0.1.
This ensures that only interconnector links are used as a network topology for CO2 and H2 pipelines.
The biomass transport is now restricted to bus regions that are next to each other excluding any interconnector transport links.

Before asking for a review for this PR make sure to complete the following checklist:

• Workflow with target rule ariadne_all completes without errors
• The logic of export_ariadne_variables has been adapted to the changes
  not applicable
• One or several figures that validate the changes in the PR have been posted as a comment
• A brief description of the changes has been added to Changelog.md
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• The latest main has been merged into the PR
• The config has a new prefix of the format YYYYMMDDdescriptive_title
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