Use dedicated elasticsearch image for observabilitySRE smoke testing (#17627)

* Use dedicated elasticsearch image for observabilitySRE smoke testing

The ES team has started publishing a purpose built image for the fedramp high
project. Update our smoke test stack to use this container.

* Override default entrypoint into elasticsearch container

The new image does not provide the stub `/app/elasticsearch.sh` file
https://github.com/elastic/elasticsearch/blob/1a1763c591c4c32bf66f0df3bce2040e8f19a1a2/distribution/docker/README.md?plain=1#L16-L19
previously available. This commit overrides the entrypoint to avoid needing that
file. See: https://github.com/elastic/elasticsearch/blob/1a1763c591c4c32bf66f0df3bce2040e8f19a1a2/distribution/docker/src/docker/Dockerfile.ess#L38C5-L40C37

* Remove entrypoint workaround due to fix landing upstream

Author: donoghuc

x-pack/distributions/internal/observabilitySRE/qa/smoke/docker/docker-compose.yml

@@ -2,7 +2,7 @@ version: '3'
 
 services:
   elasticsearch:
-    image: docker.elastic.co/elasticsearch/elasticsearch-fips:8.19.0-SNAPSHOT
+    image: docker.elastic.co/cloud-release/elasticsearch-cloud-ess-fips:8.19.0-SNAPSHOT
     environment:
       - discovery.type=single-node
       - xpack.security.enabled=true