Part of #24256.
Clear up old action logs to free up storage space.
Users will see a message indicating that the log has been cleared if
they view old tasks.
<img width="1361" alt="image"
src="https://github.com/user-attachments/assets/9f0f3a3a-bc5a-402f-90ca-49282d196c22">
Docs: https://gitea.com/gitea/docs/pulls/40
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Co-authored-by: silverwind <me@silverwind.io>
(cherry picked from commit 687c1182482ad9443a5911c068b317a91c91d586)
Conflicts:
custom/conf/app.example.ini
routers/web/repo/actions/view.go
trivial context conflict
