[Consistency] [BE] Cron job to delete unused post attachments

[katsukixyz]

Context

We have implemented post deletion functionality in a previous sprint. However, we need to handle the case in which attachment deletion from the storage bucket fails during post deletion. We want to add a cron job to remove all the missed deletions so that we don't incur extra cost.

Requirements

You are to write a cron job using Netlify Scheduled Functions. This cron job should be invoked once every day and should do the following:

1. Fetch all storage bucket objects. The object keys are in the form postId/attachmentName.fileExtension.
2. Fetch all posts that are pending: false.
3. Determine the attachments (bucket objects) that are not associated with any posts.
4. Delete those attachments (retry 3 times).

For testing, you can contact your engineering leadership for our storage bucket credentials to make sure your function invocation does what it is intended to do.

Acceptance Criteria

PM

• Unused images should be garbage collected once a day via this ticket

EM

• Log any errors using Sentry
• Cron job occurs once every day
• Attachments not associated with a post are deleted correctly with error retrying logic