agent0: catch when a bot trade is below the pool config minimum transaction amount and throw a helpful error msg

[dpaiton]

the error thrown when a trade amount is too small is not easily parsed. This should be an easy thing to check in the agent class and then we can throw a more helpful message telling the user (policy writer) to ensure that their trade_amount > interface.pool_config["minimumTransactionAmount"] before they add it to the action_list