docs: update persistent script

[st0nie]

Background

Add curl retry params to avoid failure of fetching subs && Use systemd Restart=on-failure to make sure every subs fetched successfully.

Checklist

• [x] The Pull Request has been fully tested
• [ ] There's an entry in the CHANGELOGS
• [x] There is a user-facing docs PR against https://github.com/daeuniverse/dae

Full Changelogs

• [Implement ...]

Issue Reference

Closes #[issue number]

Test Result