[Fix] DCS: Fix DCS whitelist response

[artem-lifshits]

Summary of the Pull Request

Fix whitelist update status code response

PR Checklist

• Refers to: [DCS] Error creating whitelist for DCS instance - Expected HTTP response code [204] but got 200 instead #2765
• Tests added/passed.
• Documentation updated.
• Schema updated.
• Release notes added.

Acceptance Steps Performed

=== RUN   TestAccDcsInstancesV2_Whitelist
=== PAUSE TestAccDcsInstancesV2_Whitelist
=== CONT  TestAccDcsInstancesV2_Whitelist
--- PASS: TestAccDcsInstancesV2_Whitelist (286.37s)
PASS

Process finished with the exit code 0

[otc-zuul]

Build succeeded.
https://zuul.otc-service.com/t/eco/buildset/77b78c4ae4e84d2092400ea1ae8bd1fb

✔️ build-otc-releasenotes SUCCESS in 4m 04s
✔️ noop SUCCESS in 0s
✔️ otc-golangci-lint SUCCESS in 3m 01s
✔️ golang-make-test SUCCESS in 3m 47s
✔️ golang-make-vet SUCCESS in 2m 38s
✔️ tflint SUCCESS in 1m 55s
✔️ goreleaser-build SUCCESS in 7m 18s