update REALM to env var

Author: hiimkyle

oteldemo/otel-demo-collector.yaml

@@ -45,7 +45,7 @@ agent:
             action: upsert              
     exporters:
       otlphttp:
-        traces_endpoint: "https://ingest.{REALM}.signalfx.com/v2/trace/otlp"
+        traces_endpoint: "https://ingest.${REALM}.signalfx.com/v2/trace/otlp"
         compression: gzip
         headers:
           "X-SF-Token": "${SPLUNK_OBSERVABILITY_ACCESS_TOKEN}"