Add context cancellation to backup routines about ponzu

[eticzon]

Hi @nilslice! Would you mind if I have crack at this? I want to trial ponzu as a CMS for personal projects. What better way to learn that to dive right in the codebase! 😄

[nilslice]

Hey @eticzon - please do! Thank you & let me know if you have any questions.

[nilslice]

Hi @eticzon - checking in with you on the status of this in case you had made some progress or needed help? I'll hopefully have some time this weekend for issue clean-up and this PR is on my list to get done sooner than later.

[eticzon]

Hey @nilslice! Apologies for the delay. Yup, just familiarising myself with the overall project structure and all. I should be able to create a PR before the weekend.

[nilslice]

Awesome. I didn't mean any rush, just figured I'd ask and avoid duplicating efforts. Thank you!