[WebSocket] Add redeliveryCount property to messages delivered throug…

…h the WebSocket service (apache#8074)

### Motivation

Currently, the redeliveryCount is not passed to consumer subscribed through the WebSocket service. Redelivery count is a useful feature which should be available.

### Modifications

A property is added to `org.apache.pulsar.websocket.data.ConsumerMessage` which is populated with the value coming from the original message coming from the Java pulsar client.

### Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

### Documentation

The corresponding documentation was updated.

pulsar-websocket/src/main/java/org/apache/pulsar/websocket/ConsumerHandler.java

@@ -165,6 +165,7 @@ private void receiveMessage() {
             dm.payload = Base64.getEncoder().encodeToString(msg.getData());
             dm.properties = msg.getProperties();
             dm.publishTime = DateFormatter.format(msg.getPublishTime());
+            dm.redeliveryCount = msg.getRedeliveryCount();
             if (msg.getEventTime() != 0) {
                 dm.eventTime = DateFormatter.format(msg.getEventTime());
             }

pulsar-websocket/src/main/java/org/apache/pulsar/websocket/ReaderHandler.java

@@ -128,6 +128,7 @@ private void receiveMessage() {
             dm.payload = Base64.getEncoder().encodeToString(msg.getData());
             dm.properties = msg.getProperties();
             dm.publishTime = DateFormatter.format(msg.getPublishTime());
+            dm.redeliveryCount = msg.getRedeliveryCount();
             if (msg.getEventTime() != 0) {
                 dm.eventTime = DateFormatter.format(msg.getEventTime());
             }

pulsar-websocket/src/main/java/org/apache/pulsar/websocket/data/ConsumerMessage.java

@@ -29,6 +29,7 @@ public class ConsumerMessage {
     public String payload;
     public Map<String, String> properties;
     public String publishTime;
+    public int redeliveryCount;
     public String eventTime;
 
     public String key;

site2/docs/client-libraries-websocket.md

@@ -159,7 +159,8 @@ Server will push messages on the WebSocket session:
   "messageId": "CAAQAw==",
   "payload": "SGVsbG8gV29ybGQ=",
   "properties": {"key1": "value1", "key2": "value2"},
-  "publishTime": "2016-08-30 16:45:57.785"
+  "publishTime": "2016-08-30 16:45:57.785",
+  "redeliveryCount": 4
 }
 ```
 
@@ -168,6 +169,7 @@ Key | Type | Required? | Explanation
 `messageId` | string | yes | Message ID
 `payload` | string | yes | Base-64 encoded payload
 `publishTime` | string | yes | Publish timestamp
+`redeliveryCount` | number | yes | Number of times this message was already delivered
 `properties` | key-value pairs | no | Application-defined properties
 `key` | string | no |  Original routing key set by producer
 
@@ -239,7 +241,8 @@ Server will push messages on the WebSocket session:
   "messageId": "CAAQAw==",
   "payload": "SGVsbG8gV29ybGQ=",
   "properties": {"key1": "value1", "key2": "value2"},
-  "publishTime": "2016-08-30 16:45:57.785"
+  "publishTime": "2016-08-30 16:45:57.785",
+  "redeliveryCount": 4
 }
 ```
 
@@ -248,6 +251,7 @@ Key | Type | Required? | Explanation
 `messageId` | string | yes | Message ID
 `payload` | string | yes | Base-64 encoded payload
 `publishTime` | string | yes | Publish timestamp
+`redeliveryCount` | number | yes | Number of times this message was already delivered
 `properties` | key-value pairs | no | Application-defined properties
 `key` | string | no |  Original routing key set by producer