Getter for current instance of the http client (#57)

In my workflow, it will be very useful to be able to get the current http client instance, change some of its settings, and them set it back

src/Client.php

@@ -157,6 +157,15 @@ public function setClient(BaseClient $client): void
         $this->httpClient = $client;
     }
 
+    /**
+     * Get current Guzzle client
+     * @return BaseClient
+     */
+    public function getClient(): BaseClient
+    {
+        return $this->httpClient;
+    }
+
     /**
      * Sends GET request to Customer.io API.
      * @param string $endpoint