Adds field to report which FST issued an archive request

eos_cta/protobuf/cta_eos.proto

@@ -41,6 +41,8 @@ message Workflow {
   string vpath                =  4;      //< vpath
   cta.common.Service instance =  5;      //< instance information
   uint64 timestamp            =  6;      //< event timestamp
+  string requester_instance   =  7;      //< For workflows submitted by the FST (i.e. archive requests):
+                                         //< hostname and instance name of the FST which submitted the request
 }
 
 message Client {