Add TransactionConflictError
TransactionConflictError is needed to make checking for retryable
transaction errors simple.
See also the discussion following
0x_05_02_00_03 MissingRequiredError
0x_05_03_00_00 TransactionError
-0x_05_03_00_01 TransactionSerializationError #SHOULD_RETRY
-0x_05_03_00_02 TransactionDeadlockError #SHOULD_RETRY
+0x_05_03_01_00 TransactionConflictError #SHOULD_RETRY
+0x_05_03_01_01 TransactionSerializationError
+0x_05_03_01_02 TransactionDeadlockError
####
