Double quote the env variable in curl command (#89279)

The env variable can contain special chacacters. Without quoting it
could mis-behave when used in the curl command of the setup docker
container.

docs/reference/setup/install/docker/docker-compose.yml

@@ -53,7 +53,7 @@ services:
         echo "Waiting for Elasticsearch availability";
         until curl -s --cacert config/certs/ca/ca.crt https://es01:9200 | grep -q "missing authentication credentials"; do sleep 30; done;
         echo "Setting kibana_system password";
-        until curl -s -X POST --cacert config/certs/ca/ca.crt -u elastic:${ELASTIC_PASSWORD} -H "Content-Type: application/json" https://es01:9200/_security/user/kibana_system/_password -d "{\"password\":\"${KIBANA_PASSWORD}\"}" | grep -q "^{}"; do sleep 10; done;
+        until curl -s -X POST --cacert config/certs/ca/ca.crt -u "elastic:${ELASTIC_PASSWORD}" -H "Content-Type: application/json" https://es01:9200/_security/user/kibana_system/_password -d "{\"password\":\"${KIBANA_PASSWORD}\"}" | grep -q "^{}"; do sleep 10; done;
         echo "All done!";
       '
     healthcheck: