exchanges: shift GetDefaultConfig wrapper function to exchange.go (#1472)

* Shift wrapper function GetDefaultConfig to exchange.Base method definition, to ensure set defaults doesn't get called twice and to reduce code

* rm alphapoint bootstrap method as is defined as exchange.Base method

* add tests

* glorious: make it a function and make it IBOTEXCHANGE

---------

Co-authored-by: shazbert <ryan.oharareid@thrasher.io>

engine/helpers.go

@@ -1054,7 +1054,7 @@ func NewExchangeByNameWithDefaults(ctx context.Context, name string) (exchange.I
 	if err != nil {
 		return nil, err
 	}
-	defaultConfig, err := exch.GetDefaultConfig(ctx)
+	defaultConfig, err := exchange.GetDefaultConfig(ctx, exch)
 	if err != nil {
 		return nil, err
 	}