Add a rake task for reslugging a document
Add a rake task for reslugging a document

Instead of running data_migration to reslug a document, now a rake task
can be ran by inputting the old slug and the new desired slug. This
reindexes the document in elasticsearch, republishes to pub API and
publishes a redirect content item to pub API.

alphagov/whitehall,alphagov/whitehall,alphagov/whitehall,alphagov/whitehall