Map the DiscreteMeasurements powsybl-core extension

[HugoKulesza]

Describe the current behavior

The DiscreteMeasurements extension of ppowsybl-core may currently be read and written by the underlying powsybl methods, but it is not possible to see it using the get_extension method

Describe the expected behavior

We should be able to see the DiscreteMeasurement extensions as a dataframe in python

Describe the motivation

No response

Extra Information

No response