Add test for compute server external event API

Adding test as well as the service client for the compute
server external event API
- https://docs.openstack.org/api-ref/compute/?expanded=run-events-detail#run-events

Change-Id: I1c9a99d036de760a15a5725db87ca4e9d6f2263d
diff --git a/releasenotes/notes/add-server-external-events-client-c86b269b0091077b.yaml b/releasenotes/notes/add-server-external-events-client-c86b269b0091077b.yaml
new file mode 100644
index 0000000..2af8e95
--- /dev/null
+++ b/releasenotes/notes/add-server-external-events-client-c86b269b0091077b.yaml
@@ -0,0 +1,5 @@
+---
+features:
+  - |
+    The ``server_external_events`` tempest client for compute
+    Server External Events API is implemented in this release.