enhance: Add 2 time helpers for average and median (#3748)

* enhance: Add averagetime function which allows to compute averagetime span

* enhance: lint

* enhance: Add median function and act on @mmetc feedback

* enhance: NIT on tests

* enhance: switch to []time.Time instead and handle using expr map which returns interfaces

* enhance: Add a bunch of test cases

* enhance: Rename *duration to *interval

Author: LaurenceJJones

pkg/exprhelpers/expr_lib.go

@@ -517,6 +517,22 @@ var exprFuncs = []exprCustomFunc{
 			new(func(*http.Request) string),
 		},
 	},
+	{
+		name:     "AverageInterval",
+		function: AverageInterval,
+		signature: []any{
+			new(func([]time.Time) time.Duration),
+			new(func([]interface{}) time.Duration),
+		},
+	},
+	{
+		name:     "MedianInterval",
+		function: MedianInterval,
+		signature: []any{
+			new(func([]time.Time) time.Duration),
+			new(func([]interface{}) time.Duration),
+		},
+	},
 }
 
 //go 1.20 "CutPrefix":              strings.CutPrefix,