[v11.0.x] Alerting: Use expected field name for receiver in HCL export (#87075)

Alerting: Use expected field name for receiver in HCL export (#87065)

* Use expected field name for receiver in hcl

Terraform provider expects `contact_point` instead of `receiver` in
notification settings on a rule.

(cherry picked from commit 70ff229bed)

Co-authored-by: William Wernert <william.wernert@grafana.com>

pkg/services/ngalert/api/test-data/post-rulegroup-101-export.hcl

@@ -79,7 +79,7 @@ resource "grafana_rule_group" "rule_group_0000" {
     is_paused      = false
 
     notification_settings {
-      receiver            = "Test-Receiver"
+      contact_point       = "Test-Receiver"
       group_by            = ["alertname", "grafana_folder", "test"]
       group_wait          = "1s"
       group_interval      = "5s"