Allow passing a test user home

Author: adwsingh

mcp/mcp-cli-api/src/main/java/software/amazon/smithy/java/mcp/cli/ConfigUtils.java

@@ -88,7 +88,10 @@ private static Path getSmithyMcpCliHome() {
     }
 
     public static Path resolveFromHomeDir(String... paths) {
-        String userHome = System.getProperty("user.home");
+        String userHome = System.getenv("TEST_USER_HOME");
+        if (userHome == null) {
+            userHome = System.getProperty("user.home");
+        }
         return Paths.get(userHome, paths);
     }