Elasticsearch 7.5.1 release by Elastic

The Dockerfile was kept as aligned as possible with our existing Dockerfiles [1].

Notable changes from the existing 7.5.1 release include:

• using registry.access.redhat.com instead of nexus_doc as BASE_REGISTRY
• using the non OSS version : this version
• still using the tar.gz distribution instead of rpm
• minor changes in the prebuild.sh script
• removed the discovery.seed_hosts: 0.0.0.0:9300 from the config/elasticsearch.yml
• different healthcheck

[1] https://github.com/elastic/dockerfiles/blob/7.5/elasticsearch/Dockerfile