docs: Update documentation for GET /templates (#504)

Author: LinkedList

USAGE.md

@@ -5206,6 +5206,7 @@ Transactional templates are templates created specifically for transactional ema
     Request request = new Request();
     request.setMethod(Method.GET);
     request.setEndpoint("templates");
+    request.addQueryParam("generations", "legacy,dynamic")
     Response response = sg.api(request);
     System.out.println(response.getStatusCode());
     System.out.println(response.getBody());

examples/templates/templates.java

@@ -42,6 +42,7 @@ public static void main(String[] args) throws IOException {
       Request request = new Request();
       request.setMethod(Method.GET);
       request.setEndpoint("templates");
+      request.addQueryParam("generations", "legacy,dynamic")
       Response response = sg.api(request);
       System.out.println(response.getStatusCode());
       System.out.println(response.getBody());