add tasks / job to migrate pjs under namespace

lib/tasks/pjs.rake

@@ -0,0 +1,25 @@
+namespace :pjs do
+  task stats: :environment do
+  end
+
+  desc <<~EOD
+    bin/rake 'pjs:migrate['aa']'
+    bin/rake 'pjs:migrate['aa-ab-ac']'
+  EOD
+  task :migrate, [:prefixes] => :environment do |_t, args|
+    # [a-b] => "key LIKE 'a%' or key LIKE 'b%'"
+    prefix_like_query = args[:prefixes]
+      .split('-')
+      .map { "key LIKE '#{_1}%'" }
+      .join(' or ')
+
+    blobs = ActiveStorage::Blob
+      .where(prefix_like_query)
+      .where.not("key LIKE '%/%'") # do not touch already moved blob
+
+    blobs_count = blobs.count
+    rake_puts "targeted prefix: #{args[:prefixes]}, #{blobs_count} blobs"
+
+    blobs.in_batches { |batch| batch.ids.each { |id| PjsMigrationJob.perform_later(id) } }
+  end
+end