workstations: add creator policy admin setting

[chucknthem]

Summary

Expose grant_workstation_admin_role_on_create on google_workstations_workstation_config for both the GA and beta providers. Add create-to-update sample coverage so generated acceptance tests verify the field can be changed in place.

Tests

• make test
• targeted GA WorkstationConfig generation
• targeted beta WorkstationConfig generation
• verified both generated providers contain the schema field and generated update test

workstations: added `grant_workstation_admin_role_on_create` field to `google_workstations_workstation_config` resource

[github-actions]

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[chucknthem]

agentd

Asset	Viewer	Owner
🖥 Agent	open	open
📄 Document	open	open

[github-actions]

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