Move remote cluster settings to the ES settings reference

[shainaraskas]

need to move this page to the reference

Originally posted by @shainaraskas in #443 (comment)

[eedugon]

I'll try to move this forward in this sprint as I'm doing a lot of changes to remote clusters docs and I also need to apply some other changes to Elasticsearch reference docs.

[eedugon]

Besides the settings reported in this issue: https://www.elastic.co/docs/deploy-manage/remote-clusters/remote-clusters-settings

We also have the newest settings available in this doc: https://www.elastic.co/docs/reference/elasticsearch/configuration-reference/networking-settings#remote-cluster-network-settings

So we have to clarify how to organize them at destination. My suggestion would be a "Remote cluster" settings section in ES reference docs and check with dev team if it's all right to move the advanced remote cluster settings (API key based auth) from network settings to this new dedicated section for remote clusters.

And we also need to check if we are not missing any setting (such as remote_cluster_client.*).

[eedugon]

Final PR will be #3347