[Doc] Java API: add search templates

Closes elastic#7321.

(cherry picked from commit ee108e5)

docs/java-api/search.asciidoc

@@ -145,3 +145,70 @@ DateHistogram agg2 = sr.getAggregations().get("agg2");
 
 See <<java-aggs,Aggregations Java API>>
 documentation for details.
+
+[[java-search-template]]
+=== Using Search Templates
+
+See {ref}/search-template.html[Search Template] documentation
+
+Define your template parameters as a `Map<String,String>`:
+
+[source,java]
+--------------------------------------------------
+Map<String, String> template_params = new HashMap<>();
+template_params.put("param_gender", "male");
+--------------------------------------------------
+
+You can use your stored search templates in `config/scripts`.
+For example, if you have a file named `config/scripts/template_gender.mustache` containing:
+
+[source,js]
+--------------------------------------------------
+{
+    "template" : {
+        "query" : {
+            "match" : {
+                "gender" : "{{param_gender}}"
+            }
+        }
+    }
+}
+--------------------------------------------------
+
+Execute it with:
+
+[source,java]
+--------------------------------------------------
+SearchResponse sr = client.prepareSearch()
+        .setTemplateName("template_gender")
+        .setTemplateType(ScriptService.ScriptType.FILE)
+        .setTemplateParams(template_params)
+        .get();
+--------------------------------------------------
+
+You can also store your template in a special index named `.scripts`:
+
+[source,java]
+--------------------------------------------------
+client.preparePutIndexedScript("mustache", "template_gender",
+        "{\n" +
+        "    \"template\" : {\n" +
+        "        \"query\" : {\n" +
+        "            \"match\" : {\n" +
+        "                \"gender\" : \"{{param_gender}}\"\n" +
+        "            }\n" +
+        "        }\n" +
+        "    }\n" +
+        "}").get();
+--------------------------------------------------
+
+To execute an indexed templates, use `ScriptService.ScriptType.INDEXED`:
+
+[source,java]
+--------------------------------------------------
+SearchResponse sr = client.prepareSearch()
+        .setTemplateName("template_gender")
+        .setTemplateType(ScriptService.ScriptType.INDEXED)
+        .setTemplateParams(template_params)
+        .get();
+--------------------------------------------------