autofailover timeout can be set to 1s

We need to update the documentation to mention that cusotmers can set a autofailover timeout of 1sec. Note: this can be done only from REST API and couchbase -cli , and it will not be allowed in the UI.

Also, we should make an explicit warning that before setting autofailover timeout to 1s, the cutomer to should appropriately size the nodes(CPU, memory, network) such that ns_server is starved leading to autofailovers.