Add acknowledge request parameter to Start Trial API

[russcam]

Relates: elastic/elasticsearch#30135
Documentation: https://www.elastic.co/guide/en/elasticsearch/reference/current/start-trial.html

acknowledge request query string parameter is required in 6.3.0+. This should be picked up when upgrading the REST API specs.

[Mpdreamz]

This should be in the 6.3 branch now.

[russcam]

Closing as this now exists in 6.3 branch from codegen