feat(workspace): add new resource to amanage ou

[wuzhuanhong]

What this PR does / why we need it:
Add new resource to amage OU.

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.
2. add corresponding document and acceptance test.

PR Checklist

• Tests added/passed.

./scripts/coverage.sh -o workspace -f TestAccDesktop_
Prepare to calculate the coverage the following command:
TF_ACC=1 go test "./huaweicloud/services/acceptance/workspace" -v -coverprofile="./huaweicloud/services/acceptance/workspace/workspace_coverage.cov" -coverpkg="./huaweicloud/services/workspace" -run TestAccDesktop_ -timeout 360m -parallel 10
=== RUN   TestAccDesktop_basic
--- PASS: TestAccDesktop_basic (2167.89s)
=== RUN   TestAccDesktop_UpdateWithEpsId
--- PASS: TestAccDesktop_UpdateWithEpsId (1287.56s)
=== RUN   TestAccDesktop_powerAction
--- PASS: TestAccDesktop_powerAction (1638.78s)
PASS
coverage: 15.4% of statements in ./huaweicloud/services/workspace
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/workspace 5094.304s       coverage: 15.4% of statements in ./huaweicloud/services/workspace

• Documentation updated.

• Schema updated.

• CheckDeleted.

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

    ab. Related resources (parent resources) not found
    The Workspace service is disabled.
    

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

    bb. Related resources (parent resources) not found
    The Workspace service is disabled.
    

[Alice1319]

LGTM