[Draft] Asymmetrical line and two windings transformer extensions

[annetill]

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?

Yes, a PR on open-loadlfow side: powsybl/powsybl-open-loadflow#806

What kind of change does this PR introduce?

For the moment, we have two types of line and two windings transformer extensions: one for Fortescue data and another one for three phase data (called "asymmetrical").
One all needed data are modeled, a nice solution should be to have only one extension for Fortescue data and for three phase data, each object Fortescue and `` ThreePhase` seen as an optional object. But first, focus on modeling.

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:

[sonarqubecloud]

Quality Gate failed

Failed conditions
2.9% Coverage on New Code (required ≥ 80%)

See analysis details on SonarCloud

[sonarqubecloud]

Quality Gate failed

Failed conditions
74.8% Coverage on New Code (required ≥ 80%)

See analysis details on SonarCloud