feat(redis) support spec tests with redis cluster

Kong currently does not support connection to redis cluster and will
be fixed in FTI-2104.

We should support an ENV to load redis cluster seeds:
KONG_SPEC_TEST_REDIS_CLUSTER_ADDRESSES

assets/pongo_entrypoint.sh

@@ -69,6 +69,8 @@ export KONG_LOG_LEVEL=debug
 export KONG_SPEC_REDIS_HOST=redis
 # Kong test-helpers 3.0.0+
 export KONG_SPEC_TEST_REDIS_HOST=redis
+# Support Redis Cluster
+export KONG_SPEC_TEST_REDIS_CLUSTER_ADDRESSES='["rc-node-1:6379","rc-node-2:6379","rc-node-3:6379"]'
 
 # set the certificate store
 export KONG_LUA_SSL_TRUSTED_CERTIFICATE=/etc/ssl/certs/ca-certificates.crt