Adding version label in downstream build (#775)

Author: OlivierCazade

contrib/docker/Dockerfile.downstream

@@ -41,3 +41,4 @@ LABEL io.openshift.tags="network-observability-flowlogs-pipeline"
 LABEL upstream-vcs-type="git"
 LABEL upstream-vcs-ref="$COMMIT"
 LABEL description="Flow-Logs Pipeline (a.k.a. FLP) is an observability tool that consumes logs from various inputs, transform them and export logs to loki and / or time series metrics to prometheus."
+LABEL version="1.8.0"