Elasticsearch version upgrade

Current Version

• Elastic Server: 6.8.1
• Elastic Client version(OSDU Indexer service): 6.6.1

Proposed Version upgrade

• Elastic Server: 7
• Elastic Client version(OSDU Indexer service): 7

we need to upgrade the client and elastic server version, this would require the following changes...

• Update the Indexer service, code change + lib version upgrade.
• Upgraded Elastic server in all clouds(AWS, Azure, Google, and IBM..etc).