[QoS Booking] Add explicit examples for schema that use discriminators

[eric-murray]

Problem description
Swagger-UI does not reliably autogenerate valid examples for discriminator-based schema, in this case, SinkCredential, BookingNotificationEvent and Area.

Expected action
If not already defined, define complete request and response examples so that Swagger-UI displays valid requests and responses

Additional context
None

[Masa8106]

I have reviewed the existing API specification, v0.2.0-rc.1:
For sinkCredential, I will add an example into BOOKING_ACTIVATED_WITH_DEVICE_RESPONSE and BOOKING_TERMINATED.
For BookingNotificationEvent, the example is defined in BOOKING_STATUS_CHANGED_EXAMPLE.
For Area, the example is defined in BOOKING_ACTIVATED_WITH_DEVICE_RESPONSE, BOOKING_TERMINATED, and RETRIEVE_BOOKINGS_ONE_ITEM.

[Masa8106]

I will change the way forward:
For sinkCredential, I will add an request example, in order to avoid presenting it in the response due to security reason.