SLIMIT Order by Tag

__System info:__
InfluxDB v1.7

__Steps to reproduce:__
I have a database full of traffic data, in and out by host. All working fine, but I want to plot / select only the top N traffic users. SLIMIT should do this, but I need to be able to order the items by traffic (summation), before SLIMIT is applied. It doesn't seem that this is possible? For example,
`SELECT mean("value") FROM "rp2h"."rate" WHERE time > now()-2h GROUP BY time(1s), "host", "direction" LIMIT 5 SLIMIT 3`
=> I need to be able to order the data for SLIMIT, is there a way to do this?

Thanks!

The issue mentions no file, test, or entry point. Start by reproducing the InfluxDB v1.7 query and determine whether grouped results can be ordered by their aggregate before SLIMIT; done means the requested top-N ordering behavior is defined and verified.

Written by the indexing model from the issue text.