Clone header before creating exporter HTTP request

Behind http.Header is just a map and it's not safe for concurrent use.
Before this change, a panic might have occurred when doing asynchronous
HTTP exports (applies to both *http_post and *http_json_map exporters).
Cloning the header before adding it to the HTTP request has fixed this
issue.

Slightly improved the test that found this data race.

ees/httpjsonmap.go

@@ -99,7 +99,7 @@ func (httpEE *HTTPjsonMapEE) ExtraData(ev *utils.CGREvent) any { return nil }
 func (httpEE *HTTPjsonMapEE) PrepareMap(mp *utils.CGREvent) (any, error) {
 	body, err := json.Marshal(mp.Event)
 	return &HTTPPosterRequest{
-		Header: httpEE.hdr,
+		Header: httpEE.hdr.Clone(),
 		Body:   body,
 	}, err
 }
@@ -114,7 +114,7 @@ func (httpEE *HTTPjsonMapEE) PrepareOrderMap(mp *utils.OrderedNavigableMap) (any
 	}
 	body, err := json.Marshal(valMp)
 	return &HTTPPosterRequest{
-		Header: httpEE.hdr,
+		Header: httpEE.hdr.Clone(),
 		Body:   body,
 	}, err
 }

ees/httppost.go

@@ -102,7 +102,7 @@ func (httpPost *HTTPPostEE) PrepareMap(mp *utils.CGREvent) (any, error) {
 		urlVals.Set(k, utils.IfaceAsString(v))
 	}
 	return &HTTPPosterRequest{
-		Header: httpPost.hdr,
+		Header: httpPost.hdr.Clone(),
 		Body:   urlVals,
 	}, nil
 }
@@ -116,7 +116,7 @@ func (httpPost *HTTPPostEE) PrepareOrderMap(mp *utils.OrderedNavigableMap) (any,
 		urlVals.Set(strings.Join(path, utils.NestingSep), nmIt.String())
 	}
 	return &HTTPPosterRequest{
-		Header: httpPost.hdr,
+		Header: httpPost.hdr.Clone(),
 		Body:   urlVals,
 	}, nil
 }

ees/httppost_test.go

@@ -127,20 +127,39 @@ func TestHttpPostSync(t *testing.T) {
 		t.Error(err)
 	}
 
-	mp := &utils.CGREvent{
+	req1, err := exp.PrepareMap(&utils.CGREvent{
 		Event: map[string]any{
 			"Account":     "1001",
 			"Destination": "1002",
 		},
-	}
-
-	vals, err := exp.PrepareMap(mp)
+	})
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	for i := 0; i < 3; i++ {
-		go exp.ExportEvent(context.Background(), vals, "")
+	req2, err := exp.PrepareMap(&utils.CGREvent{
+		Event: map[string]any{
+			"Account":     "1001",
+			"Destination": "1003",
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	req3, err := exp.PrepareMap(&utils.CGREvent{
+		Event: map[string]any{
+			"Account":     "1003",
+			"Destination": "1001",
+		},
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	requests := []any{req1, req2, req3}
+
+	for i := range 3 {
+		go exp.ExportEvent(context.Background(), requests[i], "")
 	}
 
 	select {