[WIP] NAD custom label provider

[CBiasuzzi]

Please check if the PR fulfills these requirements

• [ ] 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?

What kind of change does this PR introduce?

feature: provides a custom implementation of the LabelProvider; it allows you to specify in a map the branch labels (and arrow directions) to display in the diagram.

Does this PR introduce a new Powsybl Action implying to be implemented in simulators or pypowsybl?

• [ ] Yes, the corresponding issue is here
• [ ] No

What is the current behavior?

What is the new behavior (if this is a feature change)?

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

• [ ] Yes
• [ ] No

If yes, please check if the following requirements are fulfilled

• [ ] The Breaking Change or Deprecated label has been added
• [ ] The migration steps are described in the following section

What changes might users need to make in their application due to this PR? (migration steps)

Other information: