Non composable type flows are not serialized

[parthbond180]

Steps to reproduce:

1. Run cordaptor in standalone mode with obligation cordapp (both corda version 4.5)
2. Error is thrown preventing Swagger UI from coming up
   {"cause":{"class":"tech.b180.cordaptor.rest.SerializationException","message":"Flow type identified as Parameterised(CordaFlowInstruction<CashExitFlow>) was not introspected as composable.\nIntrospection details: CashExitFlow)","cause":"null"},"errorType":"GENERIC_ERROR","message":"Unknown server error"}