Introduced actions and added client + chat images
This MR implements client and chat images from the demo 2023 and introduces actions.
For now, a single action to create a user exists.
Other:
- Updated template in the readme.
- Removed TODO.md
- Fixed #1 (closed)
- Using Docker CLI instead of Docker Python client
- The base image is no longer shipped with the ubuntu user
- Using EOF instead of file appending in the entrypoints