Update the autoconfig endpoint URL in AIP (#1326)

* Update 4115.md

update the autoconfig endpoint URL

Author: xmenxk

aip/auth/4115.md

@@ -51,7 +51,7 @@ is called the mTLS configuration endpoint.
 
 The URL of the MDS's mTLS configuration endpoint is: 
 ```
-http://metadata.google.internal/computeMetadata/v1/googleAutoMtlsConfiguration
+http://metadata.google.internal/computeMetadata/v1/instance/platform-security/auto-mtls-configuration
 ```
 
 The request to the MDS's mTLS configuration endpoint **should** be an HTTP GET request without any