Change cron from hourly to twicedaily fixes #1242

[dac514]

Based on: https://core.trac.wordpress.org/ticket/44370

Many of the suggestions in the WP trac ticket seem non trivial to carry out. Performance implications seem exaggerated.

Downloads are direct links. Clicking on them doesn't trigger any action. The whole mechanism is actually sort of insecure. It relies on obfuscation. Unless we check Nginx logs we can't know when a user has downloaded.

The function that does all the work. the alleged performance hog, is wp_privacy_delete_old_export_files. This function scans a dir and deletes files that are older than 3 days. The 3 days corresponds to the text sent in an email. The amount of days can be filtered by wp_privacy_export_expiration, but I guess my point is we can't change anything except when files get deleted. The cron job still needs to run.

Since there isn't anything except personal data files in exports ./wp-personal-data-exports/ I don't actually think this will cause significant performance problems?

I've changed the cron job from hourly to twicedaily which should good enough to solve "runs too much" IMHO.

[greatislander]

This looks good, but in keeping with a5e1b8f, which introduced Pressbooks\Admin\Privacy, I'd like this class to be Pressbooks\Privacy (it supports general privacy functionality, not just GDPR).

[codecov]

Codecov Report

Merging #1246 into dev will increase coverage by 0.02%.
The diff coverage is 88.88%.

@@             Coverage Diff              @@
##                dev    #1246      +/-   ##
============================================
+ Coverage     59.16%   59.19%   +0.02%     
- Complexity     3760     3769       +9     
============================================
  Files            97       97              
  Lines         16446    16460      +14     
============================================
+ Hits           9730     9743      +13     
- Misses         6716     6717       +1