feat: realtime user analytics (#5098)

Co-authored-by: Sampras Lopes <Sampras.lopes@juspay.in>

crates/analytics/src/query.rs

@@ -253,6 +253,10 @@ pub enum Aggregate<R> {
         alias: Option<&'static str>,
         percentile: Option<&'static u8>,
     },
+    DistinctCount {
+        field: R,
+        alias: Option<&'static str>,
+    },
 }
 
 // Window functions in query