Add two migrated fields to ecs-migration from elastic#9645.

Notes:

- Can't be aliased since `body` is moving to `body.content`.
- Currently only affects Packetbeat, so it's been listed only there,
even if these are ECS field defs.
- This will affect the ES Filebeat module logs as well. A note as been
added to elastic#9293, so it doesn't get forgotten.

dev-tools/ecs-migration.yml

@@ -587,13 +587,28 @@
   to: http.version
   alias: true
 
+
 # Auditbeat
 
 ## From Auditbeat's auditd module.
 - from: source.hostname
   to: source.domain
   alias: true
 
+
+# Packetbeat
+
+- from: http.request.body
+  to: http.request.body.content
+  alias6: false
+  alias: false
+
+- from: http.response.body
+  to: http.response.body.content
+  alias6: false
+  alias: false
+
+
 # Metricbeat
 
 ## Metricbeat base fields