Backport of fix where jwt clusters are generated into release/1.19.x (#21607)

backport of commit 01e9abcddb

Co-authored-by: jm96441n <john.maguire@hashicorp.com>

agent/xds/clusters.go

@@ -1006,6 +1006,8 @@ func (s *ResourceGenerator) clustersFromSnapshotAPIGateway(cfgSnap *proxycfg.Con
 
 		clusters = append(clusters, makeAPIGatewayJWKClusters(s.Logger, cfgSnap)...)
 	}
+
+	clusters = append(clusters, makeAPIGatewayJWKClusters(s.Logger, cfgSnap)...)
 	return clusters, nil
 }