Add 3 windings transformers ratio and phase tap changers

[geofjamg]

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?

No

What kind of change does this PR introduce?

Feature

What is the current behavior?

We cannot see ratio and phase tap changers and tap changers steps for 3 windings transformers.

What is the new behavior (if this is a feature change)?
Ratio and phase tap changers and tap changers steps for 3 windings transformers have been added to existing table along with 2 windings transformers. A side column has been added because a 3 windings transformer can have multiple ratio and phase tap changers on different legs. For backward compatibility reason, side has not been added to the index.

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)

• fictitious attribute has been removed from ratio and phase tap changer dataframe because in IIDM, fictitious is at identifable level (so transformer).
• rho attribute of ratio tap changer has been moved to 2 windings transformer ans 3 windings transformer (rho1, rho2 and rho3) because it is using data of transformer + ratio tap changer steps + phase tap changer steps so a calculated attribute of the transformer itself.

Other information:

[HugoKulesza]

There are just the docstrings of getter methods for rtc/ptc and steps in python to change accordingly but otherwise all is good

[sonarqubecloud]

Quality Gate passed for 'pypowsybl-parent'

Issues
10 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sonarqubecloud]

Quality Gate passed for 'pypowsybl'

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud