Reduce OAuth token cache time to 30min

It seems that even though the token is supposed to be valid for 60min, in
practice it expires before that. Reducing caching time to 30min solves the
problem (at least as far as I can tell). This should not increase too much load
as we are only calling the API twice an hour instead of once.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=186830395

java/google/registry/proxy/config/default-config.yaml

@@ -20,11 +20,15 @@ gcpScopes:
   # to authenticate.
   - https://www.googleapis.com/auth/userinfo.email
 
-# Access token is valid for 60 minutes.
+# Access token is valid for 30 minutes.
 #
+# Document says that the token should be good for 60 minutes, but in practice
+# we've run into problems with token becoming invalid before supposed expiration
+# time. 30 minutes seems to be a good compromise which guarantees token validity
+# without making many more API calls to the OAuth server.
 # See also: Data store
 # (https://developers.google.com/api-client-library/java/google-api-java-client/oauth2#data_store).
-accessTokenValidPeriodSeconds: 3600
+accessTokenValidPeriodSeconds: 1800
 
 # Access token is refreshed 1 minutes before expiry.
 #