Refactor to use the low level java rest client

*Original comment by @ph:*

Instead of using the ES output as a builder for an elasticsearch client we will now use the the low level rest client developed in https://github.com/elastic/logstash/issues/8072

This will also give us the building block to move some of the x-pack monitoring code to java.

- [ ] Use the rest client builder from core
- [ ] Implement a high level client on top of it for Pipeline and License check.
- [ ] Make the logic type safe.

Start by reading how the Elasticsearch output currently builds its client, then inspect the REST client builder from core referenced in the checklist. Trace the Pipeline and License check logic and identify the type-safety changes required. Done means the low-level client is used, high-level clients cover both checks, and the listed logic is type safe.

Written by the indexing model from the issue text.