docs: add documentation

Signed-off-by: Lídia Tarcza <100163235+diatrcz@users.noreply.github.com>

Author: diatrcz

Authentication.md

@@ -464,6 +464,13 @@ The IAM access token is added to each outbound request in the `Authorization` he
 The default value of this property is `http://169.254.169.254`. However, if the VPC Instance Metadata Service is configured
 with the HTTP Secure Protocol setting (`https`), then you should configure this property to be `https://api.metadata.cloud.ibm.com`.
 
+- serviceVersion: (optional) The VPC Instance Metadata Service version to use.
+The default value is `2022-03-01`. When set to `2025-08-26`, the authenticator will use the new API paths
+(`/identity/v1/token` and `/identity/v1/iam_tokens`) instead of the legacy paths.
+
+- tokenLifetime: (optional) The lifetime (in seconds) of the instance identity token.
+The default value is `300` seconds. This property can only be configured programmatically (not via environment variables).
+
 Usage Notes:
 1. At most one of `iamProfileCrn` or `iamProfileId` may be specified. The specified value must map
 to a trusted IAM profile that has been linked to the compute resource (virtual server instance).
@@ -491,12 +498,27 @@ ExampleService service = new ExampleService(ExampleService.DEFAULT_SERVICE_NAME,
 // 'service' can now be used to invoke operations.
 ```
 
+To use the new service version with custom token lifetime:
+```java
+// Create the authenticator with new service version.
+VpcInstanceAuthenticator authenticator = new VpcInstanceAuthenticator.Builder()
+        .serviceVersion("2025-08-26")
+        .tokenLifetime(600)
+        .build();
+```
+
 ### Configuration example
 External configuration:
 ```
 export EXAMPLE_SERVICE_AUTH_TYPE=vpc
 export EXAMPLE_SERVICE_IAM_PROFILE_CRN=crn:iam-profile-123
 ```
+To use the new service version:
+```
+export EXAMPLE_SERVICE_AUTH_TYPE=vpc
+export EXAMPLE_SERVICE_IAM_PROFILE_CRN=crn:iam-profile-123
+export EXAMPLE_SERVICE_VPC_IMS_VERSION=2025-08-26
+```
 Application code:
 ```java
 import <sdk_base_package>.ExampleService.v1.ExampleService;