swh-search: upgrade elasticsearch to 7.15.2

• specify the memory because with the new version of ES /java try to reserve as much memory as they can

Related to swh-search#3741 (closed)

---

Migrated from D6685 (view on Phabricator)

docker/docker-compose.search.yml

@@ -2,9 +2,12 @@ version: "2.1"
 
 services:
   elasticsearch:
-    image: elasticsearch:7.9.3
     env_file:
       - ./env/elasticsearch.env
+    image: elastic/elasticsearch:7.15.2
+    environment:
+      - ingest.geoip.downloader.enabled=false
+      - "ES_JAVA_OPTS=-Xms512m -Xmx512m"
     ports:
       - 9200:9200
     volumes: