PCE-GNPy adaptation for higher rates

Currently, the parameters provided by the PCE to GNPy are hardcoded for the service type and rate. Flexgrid introduction already addresses parameters associated with frequency allocation. Some adaptations must be done to handle all modulation formats and rates, considering predefined service types. For this adaptation all intermediate rates shall be considered.

Acceptance criteria : the code must not introduce any regression. Associated Junit and functional test may be adapted, when GNPy allows handling the corresponding rates and modulation format, after OpenROADM B100G specs have been modeled in GNPy.