Fix topic not shown correctly in the consumer string (apache#329)

### Motivation

`ConsumerImpl::getName()` returns a string that is used in logs to
represent the consumer. However, the topic part does not show correctly:

```
ConsumerImpl:283 | [0x6000001c88b8, consumer-1, 0] Created consumer on broker [127.0.0.1:60399 -> 127.0.0.1:6650]
```

It's because after apache#218,
the `ConsumerImpl::topic_` field becomes `std::shared_ptr` rather than a
`std::string` but it is still used to construct the `consumerStr_`.

### Modifications

Construct the `consumerStr_` using the `topic` argument in the
constructor and make `consumerStr_` const because it is never changed.

Now the logs will be like:

```
ConsumerImpl:280 | [persistent://public/default/my-topic, consumer-1, 0] Created consumer on broker [127.0.0.1:60647 -> 127.0.0.1:6650]
```

lib/ConsumerImpl.cc

@@ -84,6 +84,7 @@ ConsumerImpl::ConsumerImpl(const ClientImplPtr client, const std::string& topic,
       receiverQueueRefillThreshold_(config_.getReceiverQueueSize() / 2),
       consumerId_(client->newConsumerId()),
       consumerName_(config_.getConsumerName()),
+      consumerStr_("[" + topic + ", " + subscriptionName + ", " + std::to_string(consumerId_) + "] "),
       messageListenerRunning_(true),
       negativeAcksTracker_(client, *this, conf),
       readCompacted_(conf.isReadCompacted()),
@@ -92,10 +93,6 @@ ConsumerImpl::ConsumerImpl(const ClientImplPtr client, const std::string& topic,
       autoAckOldestChunkedMessageOnQueueFull_(conf.isAutoAckOldestChunkedMessageOnQueueFull()),
       expireTimeOfIncompleteChunkedMessageMs_(conf.getExpireTimeOfIncompleteChunkedMessageMs()),
       interceptors_(interceptors) {
-    std::stringstream consumerStrStream;
-    consumerStrStream << "[" << topic_ << ", " << subscription_ << ", " << consumerId_ << "] ";
-    consumerStr_ = consumerStrStream.str();
-
     // Initialize un-ACKed messages OT tracker.
     if (conf.getUnAckedMessagesTimeoutMs() != 0) {
         if (conf.getTickDurationInMs() > 0) {

lib/ConsumerImpl.h

@@ -215,7 +215,7 @@ class ConsumerImpl : public ConsumerImplBase {
     const int receiverQueueRefillThreshold_;
     uint64_t consumerId_;
     std::string consumerName_;
-    std::string consumerStr_;
+    const std::string consumerStr_;
     int32_t partitionIndex_ = -1;
     Promise<Result, ConsumerImplBaseWeakPtr> consumerCreatedPromise_;
     std::atomic_bool messageListenerRunning_;

lib/MessageCrypto.cc

@@ -28,7 +28,7 @@ namespace pulsar {
 
 DECLARE_LOG_OBJECT()
 
-MessageCrypto::MessageCrypto(std::string& logCtx, bool keyGenNeeded)
+MessageCrypto::MessageCrypto(const std::string& logCtx, bool keyGenNeeded)
     : dataKeyLen_(32),
       dataKey_(new unsigned char[dataKeyLen_]),
       tagLen_(16),

lib/MessageCrypto.h

@@ -49,7 +49,7 @@ class MessageCrypto {
     typedef std::map<std::string, std::string> StringMap;
     typedef std::map<std::string, std::pair<std::string, boost::posix_time::ptime>> DataKeyCacheMap;
 
-    MessageCrypto(std::string& logCtx, bool keyGenNeeded);
+    MessageCrypto(const std::string& logCtx, bool keyGenNeeded);
     ~MessageCrypto();
 
     /*