Add support Elasticsearch 6 integration to register plugins on the transport client

• Type: Feature Request
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: None
• Fix Version/s: None
• Component/s: Search Infrastructure > Elasticsearch Connector
• Labels:
  • PT-could-7.2
  • SME-could-7.2
  • ee-nf
• Priority Level: Low

1. ClientSettingsHelper.addPlugin supported in the Elasticsearch 2 integration to apply custom plugins through the SettingsContributor
2. This API was necessary for the Liferay Elastic Shield integration
3. The current Elasticsearch 6 integration does not have this API as the X-Pack Security integration no longer requires applying additional plugins on the transport client

Request: Update our API (and implementation) to let developers leverage https://github.com/elastic/elasticsearch/blob/v6.1.4/client/transport/src/main/java/org/elasticsearch/transport/client/PreBuiltTransportClient.java#L103