Support Elasticsearch v8

[p-kimberley]

Elasticsearch v8 included several changes to the REST API, in particular the removal of mapping types. See: https://www.elastic.co/guide/en/elastic-stack/current/elasticsearch-breaking-changes.html#_rest_api_changes.

This change causes errors when attempting to index documents using the current Stroom build against an Elasticsearch v8 cluster, as tracked in this issue.

To resolve this, the Stroom Elasticsearch REST client should be upgraded to >= v8.0.0.

[p-kimberley]

The Elasticsearch Java High-Level REST Client has been deprecated and is in v7 maintenance mode. Until the newer Elasticsearch Java API Client matures, including supporting features like BulkProcessor, the existing v7.x client will be used with compatibility mode enabled, to support Elasticsearch v8 clusters.

[p-kimberley]

Superseded by #2861