introduce --dry-run mode

[junyuanz1]

When I try to test specific changes with a live account, I have to comment on a few functions.

in this PR I am going to add a --dry-run CLI flag so we can see the result without executing them.

Dry run enabled, no trades will be executed.
                                                                                   Order Summary                                                                                    
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  Symbol │ Exchange │ Contract                                                                                                                            │ Action │ Price   │ Qty  
╺━━━━━━━━┿━━━━━━━━━━┿━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┿━━━━━━━━┿━━━━━━━━━┿━━━━━╸
  SGOV   │ SMART    │ Stock(conId=424099317, symbol='SGOV', exchange='SMART', primaryExchange='ARCA', currency='USD', localSymbol='SGOV',                 │ BUY    │ $100.38 │ 144  
         │          │ tradingClass='SGOV')                                                                                                                │        │         │      
         ╵          ╵                                                                                                                                     ╵        ╵         ╵      
ThetaGang is done, shutting down! Cya next time. ✨