gha: enable hubble in clustermesh upgrade/downgrade

As it simplifies troubleshooting possible connection disruptions.
However, let's configure monitor aggregation to medium (i.e., the
maximum, and default value) to avoid the performance penalty due
to the relatively high traffic load.

Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>

.github/workflows/tests-clustermesh-upgrade.yaml

@@ -150,8 +150,8 @@ jobs:
           CILIUM_DOWNGRADE_VERSION=$(contrib/scripts/print-downgrade-version.sh stable)
           echo "downgrade_version=${CILIUM_DOWNGRADE_VERSION}" >> $GITHUB_OUTPUT
 
-          # * Hubble is disabled to avoid the performance penalty in the testing
-          #   environment due to the relatively high traffic load.
+          # * Monitor aggregation is set to medium to avoid the performance penalty
+          #   in the testing environment due to the relatively high traffic load.
           # * We explicitly configure the IPAM mode to prevent it from being
           #   reset to the default value on upgrade/downgrade due to --reset-values.
           # * We explicitly configure the sync timeout to a higher value to
@@ -162,8 +162,8 @@ jobs:
           #   occurring in the meanwhile.
           CILIUM_INSTALL_DEFAULTS=" \
             --set=debug.enabled=true \
-            --set=bpf.monitorAggregation=none \
-            --set=hubble.enabled=false \
+            --set=bpf.monitorAggregation=medium \
+            --set=hubble.enabled=true \
             --set=routingMode=tunnel \
             --set=tunnelProtocol=vxlan \
             --set=ipv4.enabled=true \