Support for most recent osc-api description

[jerome-jutteau]

Hi,
Starting from osc-api 1.26.0, the yaml description introduced a breaking change by altering some types (e.g "datetime" to "date-time").
Additionally, the yaml description now make use of "oneOf" keyword which may also introduce breaking change in interface.

As type change is breaking change:

• we will have to create a new major version
• we must make sure the generator support oneOf
• we can upgrade generator version