Give an example of a single line Hash. (#9505)

Single kv hashes look like Ruby hashes, and people get confused because they don't actually support commas, to separate each pair. This adds a more explicit example under the preferred multi-line hash example.

docs/static/configuration.asciidoc

@@ -188,6 +188,8 @@ match => {
   "field2" => "value2"
   ...
 }
+# or as a single line. No commas between entries:
+match => { "field1" => "value1" "field2" => "value2" }
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