adds a branch_labels df param to the get NAD and write NAD methods

[CBiasuzzi]

Please check if the PR fulfills these requirements

• [x] The commit message follows our guidelines
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] Docs have been added / updated (for bug fixes / features)

Does this PR already have an issue describing the problem? no

What kind of change does this PR introduce? feature

What is the current behavior? No label customization available

What is the new behavior (if this is a feature change)? Adds a branch_labels parameter to the get_network_area_diagram and write_network_area_diagram. Allows you to set branch labels (on the branch and on the branch edges) from the branch_labels dataframe parameter.

Does this PR introduce a breaking change or deprecate an API?

• [ ] Yes
• [x] No