Need to support ability to configure fallback qos

[maheshc01]

In the API spec currently we accept only 1 qos value for configuring the user session. In cases where qos configuration fails for various reasons, then the session would continue to use the default qos which might severally impact the application.
As supported in SCEF spec, we should introduce a new field named "fallbackQos" which will be used to configure the user session when the primary qos value requested for fails.

[hdamker]

From MoM-2022-10-21: Backlog item as Alternative QoS class will require a discovery function of available QoS profiles first, as described in #7. Until then clear documentation what happens if requested QoS profile can not be provided by the network -> new issue #59

[hdamker]

MoM-2023-12-01: will stay in backlog, currently no use case.