[DOCS] Adds note to inference tutorial about similarity (elastic#106567)

docs/reference/tab-widgets/inference-api/infer-api-task.asciidoc

@@ -22,6 +22,13 @@ key.
 <3> The name of the embedding model to use. You can find the list of Cohere
 embedding models https://docs.cohere.com/reference/embed[here].
 
+NOTE: When using this model the recommended similarity measure to use in the
+`dense_vector` field mapping is `dot_product`. In the case of Cohere models, the
+embeddings are normalized to unit length in which case the `dot_product` and
+the `cosine` measures are equivalent.
+
+
+
 // end::cohere[]
 
 
@@ -35,8 +42,6 @@ PUT _inference/text_embedding/openai_embeddings <1>
     "service_settings": {
         "api_key": "<api_key>", <2>
         "model_id": "text-embedding-ada-002" <3>
-    },
-    "task_settings": {
     }
 }
 ------------------------------------------------------------
@@ -51,4 +56,9 @@ key.
 embedding models
 https://platform.openai.com/docs/guides/embeddings/embedding-models[here].
 
+NOTE: When using this model the recommended similarity measure to use in the
+`dense_vector` field mapping is `dot_product`. In the case of OpenAI models, the
+embeddings are normalized to unit length in which case the `dot_product` and
+the `cosine` measures are equivalent.
+
 // end::openai[]