Add playground session id

[ferranbt]

This PR adds a session ID feature to the builder-playground to better track containers across different running instances. The key changes include:

• Adding a unique session ID (UUID) to each LocalRunner instance
• Using this session ID in container labels with playground.session={sessionID}
• Modifying container filtering to use the session ID instead of just the generic "playground=true" label
• Updating the cleanup process to only stop containers belonging to the specific session

These changes solve the problem of having multiple playground instances running simultaneously by ensuring each instance only manages its own containers. Previously, all containers shared the same "playground=true" label, which could lead to one instance inadvertently affecting containers from another instance during cleanup operations.