SOL005NSFaultManagement_def.yaml: faultDetails should be an array

Please refer to the following line: https://forge.etsi.org/rep/nfv/SOL005/blob/master/src/SOL005/NSFaultManagement/definitions/SOL005NSFaultManagement_def.yaml#L101

faultDetails should be an array of strings, instead of a string.

Page 245 of the SOL005 specification has the following, which indicates a cardinality on faultDetails:

| faultDetails | String | 0..N | Provides additional information about the fault. |