feat(workspace/user): add new resource support

[Lance52259]

What this PR does / why we need it: Support for creating workspace users through terraform.

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 user resource support.

PR Checklist

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

Acceptance Steps Performed

make testacc TEST='./huaweicloud/services/acceptance/workspace' TESTARGS='-run=TestAccUser_basic'
==> Checking that code complies with gofmt requirements...
TF_ACC=1 go test ./huaweicloud/services/acceptance/workspace -v -run=TestAccUser_basic -timeout 360m -parallel 4
=== RUN   TestAccUser_basic
=== PAUSE TestAccUser_basic
=== CONT  TestAccUser_basic
--- PASS: TestAccUser_basic (24.72s)
PASS
ok      github.com/huaweicloud/terraform-provider-huaweicloud/huaweicloud/services/acceptance/workspace 24.781s