GET gateways: Fixes missing gateway models

The GET gateways endpoint has some new features! Updated the model enum with additional model values VG34M, VG54NAE, VG54FN, SG1B, SG1x, SG1G, SG1G32, VG54NAH, VG54ATT, ACCBDHE. Previously gateways with these model values would return 'none' in responses.