Add documentation for msearch (#204)

This commit adds documentation for the msearch API.
Based on feedback from StackOverflow:

https://stackoverflow.com/a/73432234/1831

api_generator/docs/functions/Elasticsearch.msearch.md

@@ -0,0 +1,49 @@
+# Examples
+
+To make a multi-search request, specify the headers and bodies
+for the search requests in the body. The body accepts a
+`Vec<T>` where `T` implements the [Body] trait.
+
+```rust,no_run
+# use elasticsearch::{Elasticsearch, Error, MsearchParts};
+# use serde_json::{json, Value};
+# async fn doc() -> Result<(), Box<dyn std::error::Error>> {
+let client = Elasticsearch::default();
+
+fn print_hits(hits: &[Value]) {
+    for hit in hits {
+        println!(
+            "id: '{}', source: '{}', score: '{}'",
+            hit["_id"].as_str().unwrap(),
+            hit["_source"],
+            hit["_score"].as_f64().unwrap()
+        );
+    }
+}
+
+let msearch_response = client
+    .msearch(MsearchParts::None)
+    .body::<JsonBody<Value>>(vec![
+        json!({"index":"cat_food"}).into(),
+        json!({"query":{"term":{"name":{"term":"Whiskers"}}}}).into(),
+        json!({"index":"cat_food"}).into(),
+        json!({"query":{"term":{"name":{"term":"Chicken"}}}}).into(),
+        json!({"index":"cat_food"}).into(),
+        json!({"query":{"term":{"name":{"term":"Turkey"}}}}).into(),
+    ])
+    .send()
+    .await?;
+
+let json: Value = msearch_response.json().await?;
+
+// iterate over the responses
+for response in json["responses"]
+    .as_array()
+    .into_iter()
+{
+    print_hits(response["hits"]["hits"].as_array().unwrap());
+}
+    
+# Ok(())
+# }
+```

elasticsearch/src/root/mod.rs

@@ -9617,7 +9617,7 @@ impl Elasticsearch {
     pub fn mget<'a, 'b>(&'a self, parts: MgetParts<'b>) -> Mget<'a, 'b, ()> {
         Mget::new(self.transport(), parts)
     }
-    #[doc = "[Msearch API](https://www.elastic.co/guide/en/elasticsearch/reference/8.15/search-multi-search.html)\n\nAllows to execute several search operations in one request."]
+    #[doc = "[Msearch API](https://www.elastic.co/guide/en/elasticsearch/reference/8.15/search-multi-search.html)\n\nAllows to execute several search operations in one request.\n\n# Examples\n\nTo make a multi-search request, specify the headers and bodies\nfor the search requests in the body. The body accepts a\n`Vec<T>` where `T` implements the [Body] trait.\n\n```rust,no_run\n# use elasticsearch::{Elasticsearch, Error, MsearchParts};\n# use serde_json::{json, Value};\n# async fn doc() -> Result<(), Box<dyn std::error::Error>> {\nlet client = Elasticsearch::default();\n\nfn print_hits(hits: &[Value]) {\n    for hit in hits {\n        println!(\n            \"id: '{}', source: '{}', score: '{}'\",\n            hit[\"_id\"].as_str().unwrap(),\n            hit[\"_source\"],\n            hit[\"_score\"].as_f64().unwrap()\n        );\n    }\n}\n\nlet msearch_response = client\n    .msearch(MsearchParts::None)\n    .body::<JsonBody<Value>>(vec![\n        json!({\"index\":\"cat_food\"}).into(),\n        json!({\"query\":{\"term\":{\"name\":{\"term\":\"Whiskers\"}}}}).into(),\n        json!({\"index\":\"cat_food\"}).into(),\n        json!({\"query\":{\"term\":{\"name\":{\"term\":\"Chicken\"}}}}).into(),\n        json!({\"index\":\"cat_food\"}).into(),\n        json!({\"query\":{\"term\":{\"name\":{\"term\":\"Turkey\"}}}}).into(),\n    ])\n    .send()\n    .await?;\n\nlet json: Value = msearch_response.json().await?;\n\n// iterate over the responses\nfor response in json[\"responses\"]\n    .as_array()\n    .into_iter()\n{\n    print_hits(response[\"hits\"][\"hits\"].as_array().unwrap());\n}\n    \n# Ok(())\n# }\n```"]
     pub fn msearch<'a, 'b>(&'a self, parts: MsearchParts<'b>) -> Msearch<'a, 'b, ()> {
         Msearch::new(self.transport(), parts)
     }