feat(admin): add user and group management (Admin Directory API)

[dl-alexandre]

Summary

Add Google Admin SDK Directory API support for user and group management in Google Workspace.

Current State

gog groups uses Cloud Identity API for listing groups and members. This proposal adds Admin Directory API for full user provisioning and group management with domain-wide admin capabilities.

Proposed Commands

gog admin users list --domain example.com
gog admin users get user@example.com
gog admin users create user@example.com --given "John" --family "Doe" --password "..."
gog admin users suspend user@example.com
gog admin groups list --domain example.com
gog admin groups members list group@example.com
gog admin groups members add group@example.com user@example.com --role MEMBER

Use Cases

• User provisioning and deprovisioning
• Onboarding/offboarding automation
• Bulk group membership management
• Admin audits and compliance

API Notes

• API: https://developers.google.com/admin-sdk/directory/reference/rest/v1/users
• Scopes: admin.directory.user, admin.directory.group
• Requires service account with domain-wide delegation (matches existing SA support)

Related

• Add GAM feature parity for Google Workspace admin commands #179 — GAM feature parity for Workspace admin (stale PR)
• Existing gog groups command (Cloud Identity API)

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I've implemented this in another Drive CLI and can share implementation details if helpful.

[salmonumbrella]

@dl-alexandre can you please make a PR for this, or add onto #179