Add JSON ITL reader support

The Juice-SOC introduced a new ITL JSON format that will be used in the next planning exercises.

The toolbox should be able to support theses inputs in addition to the current behavior.

This new approach allow to validate the ITL with a JSON schema and make it easier to parse. Currently the general JUICE ITL schema is available in https://juicesoc.esac.esa.int/data/schemas/

Majis is expected to provide its own ITL schema on top of the SOC one to add additional Majis specific constrains.

/cc @nmanaud