We need to move all maintenance scripts to use PHP 7.2 instead of HHVM.
This can be done by simply prepending `PHP=php7.2` to all the invokations of mwscript etc in the maintenance scripts.
What needs to be done in detail:
[] Separate production maintenance scripts from wikitech ones**
[] Pick a few scripts to migrate first, notify the owners, migrate
[] Migrate the wikidata dispatcher
[] Migrate all other scripts by setting php7.2 as the preferred debian alternative
[] Revert all the modifications to the scripts above as we don't need to force
[x] Some cronjobs are shared with wikitech, which has not been switched to PHP7. To avoid blocking this task we can keep production and wikitech maint jobs separate T222900
Related to: T219135:
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[] cache_warmup
[] initsitestats
[] purge_expired_userrights
[] translationnotifications
[] uploads
[] cirrussearch
[] pageassessments
[] purge_old_cx_drafts
[] update_flaggedrev_stats
[] wikidata
[] cleanup_upload_stash
[] pagetriage
[] purge_securepoll
[] updatequerypages
[] db_lag_stats
[x] jobqueue_stats (https://gerrit.wikimedia.org/r/c/operations/puppet/+/528287)
[] parsercachepurging
[x] readinglists (https://gerrit.wikimedia.org/r/c/operations/puppet/+/528282)
[] updatequerypages
[] echo_mail_batch
[] purge_abusefilter
[] refreshlinks
[] update_special_pages
[] generatecaptcha
[] purge_checkuser
[] refreshlinks
[] updatetranslationstats.pp