Corrected example for temporary pipeline (#5555)

The temporary pipeline has to be referenced with `search_pipeline` instead of `pipeline` in the JSON.

Otherwise, you get the error `{"error":{"root_cause":[{"type":"parsing_exception","reason":"Unknown key for a START_OBJECT in [pipeline].","line":8,"col":16}],"type":"parsing_exception","reason":"Unknown key for a START_OBJECT in [pipeline].","line":8,"col":16},"status":400}`.

Tested with Docker image `opensearchproject/opensearch:2.11.0`.

Signed-off-by: Tim Vossen <61426691+upwards-gravity@users.noreply.github.com>

_search-plugins/search-pipelines/using-search-pipeline.md

@@ -38,7 +38,7 @@ POST /my-index/_search
       "text_field" : "some search text"
     }
   },
-  "pipeline" : {
+  "search_pipeline" : {
     "request_processors": [
       {
         "filter_query" : {
@@ -157,4 +157,4 @@ PUT /my_index/_settings
   "index.search.default_pipeline" : "_none"
 }
 ```
-{% include copy-curl.html %}
+{% include copy-curl.html %}