This significantly rework the auto-configuration to reflect the order
in which things are expected. Rather than keeping a conceptual cycle
between the builder and the two inner classes that are processed first,
the configuration is now split in three parts:
* The builder that is required and common
* The configuration when the HighLevelClient is available
* The RestClient configuration when that's not the case
See gh-17488
fb0fccf3c7