Add live collaboration mode

[planger]

Requirements

Users should be enabled to seamlessly share their workspace, including the model files, and their diagram state, without the need for a central, proprietary model server. Within a collaboration session, participants should benefit from a shared, real-time diagram and model state, yet each maintains an individual command stack for consistent and intuitive undo/redo actions. Additional features like visible viewports and mouse positions of each participant should further boost usability and collaboration efficiency.
The extension should be compatible with any GLSP diagram editor and should support customizations on both client and server sides.

Tool integrations

To enable collaboration beyond single diagram editors, the collaboration mode should be integrated with tool-wide collaboration systems:

• VS Code LiveShare
• Eclipse Theia Collaboration mode (see also Support collaboration feature eclipse-theia/theia#13309)

Further information

This work originates from a collaboration between @hege088 and the Business Informatics Group (TU Wien) and EclipseSource.
An initial announcement can be found on the EclipseSource blog.