refactor(cdn): refactor the cache_refresh and cache_preheat resources code style

[jinyangyang222]

What this PR does / why we need it:

commit1: refactor the cache_refresh resource code style.
commit2: refactor the cache_preheat resource code style.

Which issue this PR fixes:
(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)
fixes #xxx

Special notes for your reviewer:

Release note:

refactor the `cache_refresh` and `cache_preheat` resources code style

PR Checklist

• Tests added/passed.

Test Cache Refresh

$ export HW_CDN_DOMAIN_URL=xxxxxxxxxxx
$ export HW_ENTERPRISE_PROJECT_ID_TEST=xxxxxxxxx

$ make testacc TEST="./huaweicloud/services/acceptance/cdn" TESTARGS="-run TestAccCacheRefresh_basic"
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud/services/acceptance/cdn -v -run TestAccCacheRefresh_basic -timeout 360m -parallel 4
=== RUN   TestAccCacheRefresh_basic
=== PAUSE TestAccCacheRefresh_basic
=== CONT  TestAccCacheRefresh_basic
--- PASS: TestAccCacheRefresh_basic (13.50s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/cdn       13.559s

Test Cache Preheat

$ export HW_CDN_DOMAIN_URL=xxxxxxxxxxx
$ export HW_ENTERPRISE_PROJECT_ID_TEST=xxxxxxxxx

$ make testacc TEST="./huaweicloud/services/acceptance/cdn" TESTARGS="-run TestAccCachePreheat_basic"
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud/services/acceptance/cdn -v -run TestAccCachePreheat_basic -timeout 360m -parallel 4
=== RUN   TestAccCachePreheat_basic
=== PAUSE TestAccCachePreheat_basic
=== CONT  TestAccCachePreheat_basic
--- PASS: TestAccCachePreheat_basic (62.85s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/cdn       62.899s

Test case coverage

• Documentation updated.

• Schema updated.

• CheckDeleted.

  • a. During query operation (Read Context)
    aa. Resource not found

<!-- If the resource depends the parent resource(s), please provide the related check result(s) of the CheckDeleted validation.
ab. Related resources (parent resources) not found
\>>>>>> Paste the screenshot here <<<<<<
-->

• b. During delete/disassociate/unbind operation (Delete Context)
  ba. Resource not found
  >>>>>> Paste the screenshot here <<<<<<

[Alice1319]

LGTM

[deer-hang]

/approve
/lgtm

[github-ci-robot]

This PR has been approved by: @deer-hang

/approve
/lgtm