feat(waf): add a datasource to get the global protection whitelist rule list

[ruwenqiang123]

What this PR does / why we need it:

Add a datasource to get the global protection whitelist rule list.

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:

1.support a new datasource to get the list of the global protection whitelist rules.
2.support related document and acceptance test.

PR Checklist

• [x] Tests added/passed.
• [x] Documentation updated.
• [x] Schema updated.

Acceptance Steps Performed

$ make testacc TEST="./huaweicloud/services/acceptance/waf" TESTARGS="-run TestAccDataSourceRulesGlobalProtectionWhitelist_basic"
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud/services/acceptance/waf -v -run TestAccDataSourceRulesGlobalProtectionWhitelist_basic -timeout 360m -parallel 4
=== RUN   TestAccDataSourceRulesGlobalProtectionWhitelist_basic
=== PAUSE TestAccDataSourceRulesGlobalProtectionWhitelist_basic
=== CONT  TestAccDataSourceRulesGlobalProtectionWhitelist_basic
--- PASS: TestAccDataSourceRulesGlobalProtectionWhitelist_basic (440.40s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/waf       440.495s

[deer-hang]

/approve

[jinyangyang222]

/lgtm