Termination Conditions Tutorial (#4334)

[gziz]

Why are these changes needed?

Provide an up-to-date tutorial for Termination Conditions. I tried to follow the requirements mentioned in the #4334 issue such as:

• Focus on the mechanisms of termination conditions.
• List the available built-in termination conditions.
• Note that the termination conditions reset after each run
• Provide an example of combining termination conditions.

Also provide a nit formatting fix inside _terminations.py.

Related issue number

#4334

Checks

• [ ] I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• [ ] I've added tests (if relevant) corresponding to the changes introduced in this PR.
• [ ] I've made sure all auto checks have passed.