feat(cse/kv): add new data source to query configurations

[Lance52259]

What this PR does / why we need it:
New data source supported for the CSE service that used to query managed engine configurations (KVs).

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. supports new data source.
2. supports corresponding document and acceptance test.

PR Checklist

• Tests added/passed.

./scripts/coverage.sh -o cse -f TestAccDataMicroserviceEngineConfigurations_basic
Prepare to calculate the coverage the following command:
TF_ACC=1 go test "./huaweicloud/services/acceptance/cse" -v -coverprofile="./huaweicloud/services/acceptance/cse/cse_coverage.cov" -coverpkg="./huaweicloud/services/cse" -run TestAccDataMicroserviceEngineConfigurations_basic -timeout 360m -parallel 10
=== RUN   TestAccDataMicroserviceEngineConfigurations_basic
=== PAUSE TestAccDataMicroserviceEngineConfigurations_basic
=== CONT  TestAccDataMicroserviceEngineConfigurations_basic
--- PASS: TestAccDataMicroserviceEngineConfigurations_basic (10.14s)
PASS
coverage: 20.9% of statements in ./huaweicloud/services/cse
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/cse       10.189s coverage: 20.9% of statements in ./huaweicloud/services/cse

• Documentation updated.
• Schema updated.
• CheckDeleted.

[github-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This PR has been approved by: @Lance52259