CP-49158: [later] introduce a batching delay on first response

Also introduce a batching delay on all Event.{from,next} calls, except
Event.from calls for tasks. This should help batch up multiple events from
field updates.

There are no extra delays for tasks, because these typically aren't immediately ready,
and when they are we want to immediately find out about it.

This is part of the "feature flag" that turns on the feature
(previously you could've manually edited xapi.conf to make these changes.)

Signed-off-by: Edwin Török <[email protected]>

ocaml/xapi/xapi_globs.ml

@@ -1097,7 +1097,8 @@ let make_batching name ~delay_before ~delay_between =
   (config, (name, Arg.String set, get, desc))
 
 let event_from_delay, event_from_entry =
-  make_batching "event_from" ~delay_before:Mtime.Span.zero
+  make_batching "event_from"
+    ~delay_before:Mtime.Span.(50 * ms)
     ~delay_between:Mtime.Span.(50 * ms)
 
 let event_from_task_delay, event_from_task_entry =