feat: add user management documentation for InfluxDB Cloud Dedicated Admin UI

[MeelahMe]

Closes #6207

Overview

Adds comprehensive documentation for the new user management capabilities in the InfluxDB Cloud Dedicated Admin UI, enabling self-service user administration.

Changes

• Add detailed guide for inviting users through the Admin UI
• Document role-based permissions (Admin, Member, Auditor)
• Include invitation management workflows (send, revoke, view status)
• Explain current limitations and alternative methods
• Follow InfluxData documentation standards and patterns

Impact

• Reduces support requests for basic user management operations
• Enables customers to manage users independently through the Admin UI
• Provides clear guidance on role assignments and permissions

Resolves #6207

[Copilot]

Pull Request Overview

Adds comprehensive user management documentation for the InfluxDB Cloud Dedicated Admin UI to enable self-service user administration. This documentation reduces the need for support requests by providing clear guidance on inviting users, managing invitations, and understanding role-based permissions through the web interface.

• Creates detailed Admin UI user management guide covering invitation workflows and role assignments
• Updates parent page to differentiate between self-service Admin UI operations and support-required tasks
• Documents current limitations and alternative methods for advanced operations

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
content/influxdb3/cloud-dedicated/admin/users/admin-ui.md	New comprehensive guide for Admin UI user management features
content/influxdb3/cloud-dedicated/admin/users/_index.md	Updated to reorganize content and distinguish Admin UI vs support methods

[jstirnaman]

This looks good, just a couple of minor fixes. Can you ask the Product Manager to review?

[Copilot]

Pull Request Overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

[Copilot]

The note block uses GitHub-style alert syntax > [!Note] instead of the Hugo shortcode format used elsewhere in the file. For consistency with the rest of the documentation (like line 68-71), this should use the Hugo shortcode format: {{% note %}} and {{% /note %}}.

Suggested change

	> [!Note]
	> #### Role assignment
	>
	> User roles are assigned when sending invitations and cannot currently be changed through the Admin UI.
	> To modify a user's role, [contact InfluxData support](https://support.influxdata.com).
	{{% note %}}
	**Role assignment**
	User roles are assigned when sending invitations and cannot currently be changed through the Admin UI.
	To modify a user's role, [contact InfluxData support](https://support.influxdata.com).
	{{% /note %}}

[Copilot]

The note block uses GitHub-style alert syntax > [!Note] instead of the Hugo shortcode format used elsewhere in the documentation. This should be consistent with the Hugo shortcode format: {{% note %}} and {{% /note %}}.