add: example of lgbm

[hamster-86]

add an example of the terminator in using lightgbm

[g-votte]

@hamster-86 Thanks for your PR!

I have a couple of comments:

• Instead of putting the example under terminator, how about doing it under lightgbm so that to appeal more to lightgbm users?
• The black command seems to be failing. Please modify the code according to this error message: https://github.com/optuna/optuna-examples/actions/runs/6360533473/job/17274366027?pr=207

FYI: You can see which commands run with the Checks job here: https://github.com/optuna/optuna-examples/blob/main/.github/workflows/checks.yml

[g-votte]

Let me close this PR, since it is addressed in #209 and #210 instead.