api: admin/datastore: enable streaming for some api calls

namely /admin/datastore/{store}/snapshots
and /nodes/{node}/tasks

since those are api calls where the result can get quite large
with this change, the serialization is now streaming instead of making
a `Value` in memory.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/api2/node/tasks.rs

@@ -380,6 +380,7 @@ fn stop_task(
 }
 
 #[api(
+    streaming: true,
     input: {
         properties: {
             node: {