CNV#73301: Deprecation notice of ephemeral hotplug volumes

Co-authored-by: Shikha Jhala <sjhala@redhat.com>

Author: rheslop

virt/release_notes/virt-4-21-release-notes.adoc

@@ -89,6 +89,17 @@ link:https://issues.redhat.com/browse/CNV-66115[CNV-66115]
 [id="virt-4-21-deprecated_{context}"]
 == Deprecated features
 
+The `HotplugVolume` feature gate is deprecated::
+
+The `HotplugVolume` feature gate, which allows you to add storage without restarting your VM, is deprecated and will be removed in a future release. This feature gate will be replaced by `DeclarativeHotplugVolumes`.
++
+[NOTE]
+====
+`DeclarativeHotplugVolumes` does not support hot plugging ephemeral volumes. Ephemeral volumes are hot plugged to a VMI and do not persist in the owner VM. Existing ephemeral volumes that are hot plugged are automatically detached after you switch to the `DeclarativeHotplugVolumes` feature gate.
+====
+
+link:https://issues.redhat.com/browse/CNV-73301[CNV-73301]
+
 [id="virt-4-21-removed_{context}"]
 == Removed features