currently we only return a stringified version of the original error code returned by the E2 node

There's a workaround that the excact error code is now added in text format (JSON) as described here: https://docs.o-ran-sc.org/projects/o-ran-sc-ric-plt-submgr/en/latest/user-guide.html in "special notes" with this example

Example descriptive error string for RICSubscriptionResponse:

Error cause RICSubscriptionResponse partially accepted: ActionNotAdmittedList: [\{"ActionId":1,"Cause":{"Content":1,"Value":8}}]

Example descriptive error string for RICSubscriptionFailure:

Error cause RICSubscriptionFailure: ActionNotAdmittedList: [\{"ActionId":1,"Cause":{"Content":5,"Value":1}}]