Add a new REST API endpoint 'GET _cat/cluster_manager' as the replacement of 'GET _cat/master' (#2404)

* Add a new path `/_cat/cluster_manager` for the REST request handler `RestMasterAction`
* Deprecate the existing path `/_cat/master`
* Change the name of the `RestMasterAction` handler from `cat_master_action` to `cat_cluster_manager_action`
* Change the response of `GET _cat` to only show the new path `/_cat/cluster_manager`
* Rename the JSON rest-api-spec file `cat.master.json` to `cat.cluster_manager.json` and update the paths.
* Add YAML REST test. By default, it will run test for both endpoints `GET _cat/cluster_manager` and `GET _cat/master`

Signed-off-by: Tianli Feng <ftianli@amazon.com>

Author: Tianli Feng

rest-api-spec/src/main/resources/rest-api-spec/api/cat.master.json rest-api-spec/src/main/resources/rest-api-spec/api/cat.cluster_manager.json

@@ -1,17 +1,27 @@
 {
-  "cat.master":{
+  "cat.cluster_manager":{
     "documentation":{
-      "url":"https://www.elastic.co/guide/en/elasticsearch/reference/master/cat-master.html",
-      "description":"Returns information about the master node."
+      "url":"https://opensearch.org/docs/latest/opensearch/rest-api/cat/cat-master/",
+      "description":"Returns information about the cluster-manager node."
     },
     "stability":"stable",
     "url":{
       "paths":[
         {
-          "path":"/_cat/master",
+          "path":"/_cat/cluster_manager",
           "methods":[
             "GET"
           ]
+        },
+        {
+          "path":"/_cat/master",
+          "methods":[
+            "GET"
+          ],
+          "deprecated":{
+            "version":"2.0.0",
+            "description":"To promote inclusive language, please use '/_cat/cluster_manager' instead."
+          }
         }
       ]
     },
@@ -22,7 +32,7 @@
       },
       "local":{
         "type":"boolean",
-        "description":"Return local information, do not retrieve the state from master node (default: false)"
+        "description":"Return local information, do not retrieve the state from cluster-manager node (default: false)"
       },
       "master_timeout":{
         "type":"time",

rest-api-spec/src/main/resources/rest-api-spec/test/cat.cluster_manager/10_basic.yml

@@ -0,0 +1,46 @@
+setup:
+  - skip:
+      features: allowed_warnings
+
+---
+"Help":
+  - skip:
+      version: " - 1.4.99"
+      reason: "path _cat/cluster_manager is introduced in 2.0.0"
+
+  - do:
+      cat.cluster_manager:
+        help: true
+      allowed_warnings:
+        - '[GET /_cat/master] is deprecated! Use [GET /_cat/cluster_manager] instead.'
+
+  - match:
+      $body: |
+        /^  id       .+ \n
+            host     .+ \n
+            ip       .+ \n
+            node     .+ \n
+        
+        $/
+
+---
+"Test cat cluster_manager output":
+  - skip:
+      version: " - 1.4.99"
+      reason: "path _cat/cluster_manager is introduced in 2.0.0"
+
+  - do:
+      cat.cluster_manager: {}
+      allowed_warnings:
+        - '[GET /_cat/master] is deprecated! Use [GET /_cat/cluster_manager] instead.'
+
+  - match:
+      $body: |
+        /^
+          ( \S+                     \s+ # node id
+            [-\w.]+                 \s+ # host name
+            (\d{1,3}\.){3}\d{1,3}   \s+ # ip address
+            [-\w.]+                     # node name
+            \n
+          )
+        $/

server/src/main/java/org/opensearch/rest/action/cat/RestMasterAction.java

@@ -50,18 +50,19 @@
 public class RestMasterAction extends AbstractCatAction {
 
     @Override
-    public List<Route> routes() {
-        return singletonList(new Route(GET, "/_cat/master"));
+    public List<ReplacedRoute> replacedRoutes() {
+        // The deprecated path will be removed in a future major version.
+        return singletonList(new ReplacedRoute(GET, "/_cat/cluster_manager", "/_cat/master"));
     }
 
     @Override
     public String getName() {
-        return "cat_master_action";
+        return "cat_cluster_manager_action";
     }
 
     @Override
     protected void documentation(StringBuilder sb) {
-        sb.append("/_cat/master\n");
+        sb.append("/_cat/cluster_manager\n");
     }
 
     @Override