refact(pcf): Move API handling into separate classes

src/api-server/CMakeLists.txt

src/api-server/api/SMPoliciesCollectionApi.cpp

src/api-server/api/SMPoliciesCollectionApi.h

src/api-server/handler/api_response.h

...ver/handler/individual_sm_policy_document_api_handler.cpp

...erver/handler/individual_sm_policy_document_api_handler.h

...api-server/handler/sm_policies_collection_api_handler.cpp

src/api-server/handler/sm_policies_collection_api_handler.h

src/api-server/impl/IndividualSMPolicyDocumentApiImpl.cpp

src/api-server/impl/IndividualSMPolicyDocumentApiImpl.h

src/api-server/impl/SMPoliciesCollectionApiImpl.cpp

src/api-server/impl/SMPoliciesCollectionApiImpl.h

src/oai_pcf/CMakeLists.txt