Merge branch...

Merge branch 'Rel18_correction_to_Schema_definition_Issues_for_SubNetwork_and_ManagedElement_of_OpenAPI_SS' into 'Integration_Rel18_SA5_153_YAML'

Rel18 correction to schema definition issues for sub network and managed element of open api ss (TS28.104 CR0078, TS28.105 CR0073, TS28.312 CR0202, TS28.536 CR0066, TS28.538 CR0056, TS28.541 CR1140, TS28.623 CR0307)

See merge request !979