support IP whitelists for DCS redis 4.0 and 5.0 version

[ShiChangkuo]

fixes #505

the acceptance testing result as follows:

$ make testacc TEST='./huaweicloud' TESTARGS='-run TestAccDcsInstancesV1_whitelists'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud -v -run TestAccDcsInstancesV1_whitelists -timeout 360m
=== RUN   TestAccDcsInstancesV1_whitelists
--- PASS: TestAccDcsInstancesV1_whitelists (52.50s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud       52.533s