Add example for contact group data source

Author: tomasbasham

examples/data-sources/statuscake_contact_group/data-source.tf

@@ -0,0 +1,7 @@
+data "statuscake_contact_group" "developers" {
+  id = "123456"
+}
+
+output "developers_contact_group_name" {
+  value = data.statuscake_contact_group.developers.name
+}