Add support for HTTP compression level

[inqueue]

Please add support for setting the compression level for HTTP requests. Once implemented, the user would be able to set the compression level to a value supported by gzip; i.e., 0 to 9.

This is part of a downstream request for ES Rally to support configuring the compression level.

[ruflin]

++ on getting support for this. Today with Elastic Agent / Beats we let configure our users the compression level from 0 to 9 and we want to test what impact it has on the ingest performance in Elasticsearch with rally: elastic/rally#1713