needs a better discussion on kvEndpoints

In discussion with Muneeb Master [X], end users can't get out of this page an understanding of how a single endpoint is pipelined. They think (erroneously) they need a socket per thread or concurrent call.

https://docs.couchbase.com/java-sdk/2.7/client-settings.html#java-performance-options-ref makes it clear that you shouldn't adjust without testing and that 1 is correctly a sane default. But, it's not referenced from here.

Also, Muneeb Master [X] argues that it doesn't describe how to profile or benchmark. I think that's a bit detailed for our documentation, but a further hint could be good.

We can also refer to MB-10291 which is the usual flaw that requires kvEndpoints to be tuned.