Forwarding logs to Splunk via Vector returns HTTP 404 in RHOCP 4

Issue

• Log forwarding to Splunk via Vector log collector is configured but there are no logs being forwarded.

• Following log entries can be found in log collector pods:

  [user@server]$ oc -n openshift-logging logs collector-xfdxr | tail -20
  Defaulted container "collector" out of: collector, logfilesmetricexporter
  2023-03-21T08:44:45.236988Z ERROR sink{component_kind="sink" component_id=remote_splunk component_type=splunk_hec component_name=remote_splunk}:request{request_id=45340}: vector::sinks::util::retries: Not retriable; dropping the request. reason="response status: 404 Not Found"
  2023-03-21T08:44:46.498813Z ERROR sink{component_kind="sink" component_id=remote_splunk component_type=splunk_hec component_name=remote_splunk}:request{request_id=45341}: vector::sinks::util::retries: Not retriable; dropping the request. reason="response status: 404 Not Found"
  [...]