Add migration service and task

lib/tasks/deployment/20200625113026_migrate_revisions.rake

@@ -0,0 +1,22 @@
+namespace :after_party do
+  desc 'Deployment task: migrate_revisions'
+  task migrate_revisions: :environment do
+    puts "Running deploy task 'migrate_revisions'"
+
+    procedures = Procedure.with_discarded.where(draft_revision_id: nil)
+    progress = ProgressReport.new(procedures.count)
+
+    puts "Processing procedures"
+    procedures.find_each do |procedure|
+      RevisionsMigration.add_revisions(procedure)
+      progress.inc
+    end
+    progress.finish
+
+    TmpDossiersMigrateRevisionsJob.perform_later([])
+
+    # Update task as completed.  If you remove the line below, the task will
+    # run with every deploy (or every time you call after_party:run).
+    AfterParty::TaskRecord.create version: '20200625113026'
+  end
+end