Update docs to include recommended configuration for timeout/keepalive based on ES recomendations

[JoshMock]

The Elasticsearch docs were recently updated to include more clear recommendations on the proper timeout and keepalive settings for clients that connect to ES. In discussing these recommendations with @DaveCTurner, the devtools team established that most clients do not follow them by default.

Since it would likely be a breaking change to update the defaults, we need to at least document in the JS client how to properly follow these recommendations. And when 9.0 comes out, we can update the client to follow these recs.

See also:

• ES networking configuration docs

[JoshMock]

@jloleysens