Also add an ERROR_codes.txt file for mgmd

Index: ndb-work/storage/ndb/src/mgmsrv/ERROR_codes.txt
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storage/ndb/src/mgmsrv/Services.cpp:
  WL#3704 mgmapi timeouts: renumber mgmd err insert to not have duplicates.
storage/ndb/test/ndbapi/testMgm.cpp:
  WL#3704 mgmapi timeouts: renumber mgmd err insert to not have duplicates.
storage/ndb/src/mgmsrv/ERROR_codes.txt:
  WL#3704 mgmapi timeouts: renumber mgmd err insert to not have duplicates.