metrics: peak gauges for in-flight queries, stream connections and the query log queue

src/server/doh_server.zig

@@ -148,6 +148,10 @@ pub const DohServer = struct {
         return self.core.boundAddress();
     }
 
+    pub fn connectionsPeak(self: *const DohServer) u64 {
+        return self.core.connectionsPeak();
+    }
+
     pub fn snapshotStats(self: *const DohServer) Snapshot {
         const core = &self.core.stats;
         return .{