[Feature Request] Allow grouping clients in FRPS dashboard

Describe the feature request

It would be nice to be able to group multiple clients into "folders" or "groups" in the frps client list.

Describe alternatives you've considered

Just a nice to have, this software is amazing as it is today. Thanks for the great work.

Affected area

• Docs
• Installation
• Performance and Scalability
• Security
• User Experience
• Test and Release
• Developer Infrastructure
• Client Plugin
• Server Plugin
• Extensions
• Others