Add a rake task for finding druids with replication errors ... and update replication errors wiki

[ndushay]

https://github.com/sul-dlss/preservation_catalog/wiki/Replication-errors refers to this rails console command:

druids = ZipPart.unreplicated.joins(zipped_moab_version: :preserved_object).pluck(:druid).uniq

Having a rake task for this implies it is more easily used and is also maintained code (?).

The actions for this ticket are

• to make such a rake task
• have test code for the code part if that makes sense (it seems like it's just a sql query)
• do a PR for the above
• update the wiki https://github.com/sul-dlss/preservation_catalog/wiki/Replication-errors to use the rake task instead of the rails console command.