Migrate to new Elasticsearch client and remove all other dependencies on Elasticsearch

[hmottestad]

Related to: #4441

Migrate to the following client:

		<dependency>
			<groupId>co.elastic.clients</groupId>
			<artifactId>elasticsearch-java</artifactId>
			<version>${elasticsearch.version}</version>
		</dependency>

This should disconnect Elasticsearch from Lucene so that we no longer need to match those two versions precisely.

All licenses are either EPL 2.0 or Apache 2.0, both of which are for us to use.

It still depends on HTTP Client 4.x, but it is worth noting that 5.x is actually a new groupId and artifactId, which I hope means that we can mix and match.

[hmottestad]

Let's just hope that Elastic is done inventing new clients for a while. This will be the third client, after the Java High Level REST Client and the Transport Client.