7.5.0-pre

Pre-release version of 7.5 client.

• Support for Elasticsearch 7.5.
• Update API spec generator: The code for Elasticsearch OSS and X-Pack APIs is being generated from the rest api spec.
• Specs have been updated to address new/deprecated parameters.
• This is a pre-release, full Changelog details will be published with the final release of 7.5.0