MB-47766 Change maximum analytics replicas to 3

The real maximum for analytics replicas has been chosen to be 3. This
change enforces it.

Change-Id: If66c40a8bac23cf825374d99063319a80b02bd23
Reviewed-on: http://review.couchbase.org/c/ns_server/+/159434
Well-Formed: Build Bot <build@couchbase.com>
Tested-by: Steve Watanabe <steve.watanabe@couchbase.com>
Reviewed-by: <hareen.kancharla@couchbase.com>

src/menelaus_web_analytics.erl

@@ -22,7 +22,7 @@ get_settings() ->
 
 settings_post_validators() ->
     [validator:has_params(_),
-     validator:integer(numReplicas, 0, 16, _),
+     validator:integer(numReplicas, 0, 3, _),
      validator:unsupported(_)].
 
 update_settings(Key, Value) ->