allow support for parity '0', '1' enabling support for 2,3 drive setups (#15171)

allows for further granular setups

- 2 drives (1 parity, 1 data)
- 3 drives (1 parity, 2 data)

Bonus: allows '0' parity as well.

internal/config/storageclass/storage-class_test.go

@@ -102,7 +102,8 @@ func TestValidateParity(t *testing.T) {
 		{2, 4, true, 16},
 		{3, 3, true, 16},
 		{0, 0, true, 16},
-		{1, 4, false, 16},
+		{1, 4, true, 16},
+		{0, 4, true, 16},
 		{7, 6, false, 16},
 		{9, 0, false, 16},
 		{9, 9, false, 16},
@@ -140,7 +141,7 @@ func TestParityCount(t *testing.T) {
 				Parity: 8,
 			},
 			RRS: StorageClass{
-				Parity: 0,
+				Parity: 2,
 			},
 		}
 		// Set env var for test case 4