Centralize API version for stateful calls

The API version (currently "v1") used in stateful ChatGPT API calls has
been centralized into a constant for improved management.

Change-Id: Ifbfc0c056073d82b2a8e1c8f40c88312a5bfd18c
Signed-off-by: Patrizio <patrizio.gelosi@amarulasolutions.com>

src/main/java/com/googlesource/gerrit/plugins/chatgpt/mode/stateful/client/api/UriResourceLocatorStateful.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/chatgpt/mode/stateful/client/api/UriResourceLocatorStateful.java b/src/main/java/com/googlesource/gerrit/plugins/chatgpt/mode/stateful/client/api/UriResourceLocatorStateful.java
index b56aa43..9480d76 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/chatgpt/mode/stateful/client/api/UriResourceLocatorStateful.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/chatgpt/mode/stateful/client/api/UriResourceLocatorStateful.java
@@ -1,16 +1,18 @@
 package com.googlesource.gerrit.plugins.chatgpt.mode.stateful.client.api;
 
 public class UriResourceLocatorStateful {
+    private static final String VERSION_URI = "/v1";
+
     public static String filesCreateUri() {
-        return "/v1/files";
+        return VERSION_URI + "/files";
     }
 
     public static String assistantCreateUri() {
-        return "/v1/assistants";
+        return VERSION_URI + "/assistants";
     }
 
     public static String threadsUri() {
-        return "/v1/threads";
+        return VERSION_URI + "/threads";
     }
 
     public static String threadRetrieveUri(String threadId) {