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/engine_test.go

@@ -378,7 +378,7 @@ func TestGetDefaultConfigurations(t *testing.T) {
 				t.Skipf("skipping %s unsupported", name)
 			}
 
-			defaultCfg, err := exch.GetDefaultConfig(context.Background())
+			defaultCfg, err := exchange.GetDefaultConfig(context.Background(), exch)
 			if err != nil {
 				t.Fatal(err)
 			}