Change how access tokens are refreshed

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=212880971

java/google/registry/proxy/ProxyConfig.java

@@ -37,7 +37,7 @@ public class ProxyConfig {
 
   public String projectId;
   public List<String> gcpScopes;
-  public int accessTokenValidPeriodSeconds;
+  public int accessTokenRefreshBeforeExpirationSeconds;
   public int serverCertificateCacheSeconds;
   public Gcs gcs;
   public Kms kms;