Provide REST API methods to manage users and groups

Summary

As a Confluence System Administrator I would like to be able to manage users and groups directly from REST API endpoints. Automation and scripting of user management can be made easier with REST API.

Problem statement

User and groups management is currently not possible via REST API only. Bulk operations, automation or scripting of management actions is not currently possible when using REST API. User management was previously possible with SOAP, which has been deprecated.

Suggested Resolution

Provide methods akin to what as present with SOAP that would allow Admins to manage users and groups via REST API.

Previous Ticket Description
As Confluence is popular tool used by many users, it should provide the API to add users to groups, similar to what Jira Cloud has.