doc: add a release note about csi sidecar metrics

Added a release note for csi sidecar metrics

Signed-off-by: Nikhil-Ladha <[email protected]>

PendingReleaseNotes.md

@@ -6,5 +6,8 @@
 
 - util: a log message "Slow GRPC" is now emitted when
   CSI GRPC call outlives its deadline [PR](https://github.com/ceph/ceph-csi/pull/4847)
+- CSI metrics for sidecars are now exposed at `POD_IP`:`SIDECAR_ENDPOINT`/`metrics`
+  path. Check sidecar container spec for `SIDECAR_ENDPOINT`
+  value [PR](https://github.com/ceph/ceph-csi/pull/4887)
 
 ## NOTE