Update documentation to replace usage of `TextMentionTermination` that relies on models in favor of more robust conditions

### Confirmation

- [x] I confirm that I am a maintainer and so can use this template. If I am not, I understand this issue will be closed and I will be asked to use a different template.

### Issue body

For example, we can ask user to terminate via user proxy or use other robust and deterministic conditions. 

See discussion: 
#5836 