Fix thread target invocation in paper_trading/alpaca.py (submitOrder called immediately)

[AshutoshKumar1007]

Issue description:
In finrl/meta/paper_trading/alpaca.py, the thread is created like this:
Current pattern (runs immediately):

tSubmitOrder = threading.Thread( target=self.submitOrder( qty, self.stockUniverse[index], "buy", respSO ) )

this calls self.submitOrder(...) immediately and passes its return value as target
so the work runs on the main thread and the new thread gets None as the target.

The expected usage is to pass the function and its args separately:

tSubmitOrder = threading.Thread( target=self.submitOrder, args=(qty, self.stockUniverse[index], "buy", respSO) )
This occurs in both buy and sell sections.