🌊 Streams: Set subobjects: false (elastic#203002)

With elastic/elasticsearch#117544 fixed,
`subobjects: false` can be set on wired streams.

This allows to map fields as scalars even if they share the same prefix,
e.g.
* `deeply.nested.path` as `keyword`
* `deeply.nested.path.and.more` as `keyword`

x-pack/plugins/streams/server/lib/streams/component_templates/generate_layer.ts

@@ -36,7 +36,7 @@ export function generateLayer(
     template: {
       settings: isRoot(definition.id) ? logsSettings : {},
       mappings: {
-        subobjects: true, // TODO set to false once this works on Elasticsearch side - right now fields are not properly indexed.
+        subobjects: false,
         dynamic: false,
         properties,
       },