feat(servicestage/app): add new resource to manage applications

[Lance52259]

What this PR does / why we need it: Add new resource to manage applications and according to the ver.3 APIs.

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. add new resource to manage applications.

PR Checklist

• [x] Tests added/passed.

../coverage.sh -o servicestage -f TestAccV3Application_basic
Prepare to calculate the coverage the following command:
TF_ACC=1 go test "./huaweicloud/services/acceptance/servicestage" -v -coverprofile="./huaweicloud/services/acceptance/servicestage_coverage.cov" -coverpkg="./huaweicloud/services/servicestage" -run TestAccV3Application_basic -timeout 360m -parallel 10
=== RUN   TestAccV3Application_basic
=== PAUSE TestAccV3Application_basic
=== CONT  TestAccV3Application_basic
--- PASS: TestAccV3Application_basic (107.38s)
PASS
coverage: 9.2% of statements in ./huaweicloud/services/servicestage
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/servicestage      107.436s        coverage: 9.2% of statements in ./huaweicloud/services/servicestage

• [x] Documentation updated.
• [x] Schema updated.

• [x] CheckDeleted.

  • a. During query operation (Read Context) aa. Resource not found
  • b. During delete/disassociate/unbind operation (Delete Context) ba. Resource not found

[github-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This PR has been approved by: @Lance52259

[github-ci-robot]

This PR needs rebase.

[deer-hang]

/lgtm