Update service/solver.ml

solver instead of worker make sense.

Co-authored-by: Mark Elvers <mtelvers@users.noreply.github.com>

Author: moyodiallo

service/solver.ml

@@ -17,7 +17,7 @@ module Metrics = struct
   open Prometheus
 
   let namespace = "ocluster"
-  let subsystem = "worker"
+  let subsystem = "solver"
 
   let request_handling_total =
     let help = "Total number of handled solve requests" in