Move database clean from cron to Sidekiq scheduler

After moving the remaining tasks from schedule.rb to sidekiq.yml, we can
remove whenever and won't rely on cron any more. That will simplify the
setup and migration to a new server.

app/jobs/rake_job.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+# Executes a rake task
+class RakeJob < ApplicationJob
+  def perform(task_string)
+    Rails.application.load_tasks if Rake::Task.tasks.empty?
+
+    Rake.application.invoke_task(task_string)
+  ensure
+    name, _args = Rake.application.parse_task_string(task_string)
+    Rake::Task[name].reenable
+  end
+end

config/schedule.rb

@@ -11,10 +11,6 @@ env "MAILTO", ENV["SCHEDULE_NOTIFICATIONS"] if ENV["SCHEDULE_NOTIFICATIONS"]
 # If we use -e with a file containing specs, rspec interprets it and filters out our examples
 job_type :run_file, "cd :path; :environment_variable=:environment bundle exec script/rails runner :task :output"
 
-every 1.month, at: '4:30am' do
-  rake 'ofn:data:remove_transient_data'
-end
-
 every 1.day, at: '2:45am' do
   rake 'db2fog:clean' if ENV['S3_BACKUPS_BUCKET']
 end

config/sidekiq.yml

@@ -19,3 +19,6 @@
       every: "5m"
     OrderCycleClosingJob:
       every: "5m"
+    RakeJob:
+      args: ["ofn:data:remove_transient_data"]
+      cron: "30 4 1 * *"

spec/jobs/rake_job_spec.rb

@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require "tasks/data/remove_transient_data"
+
+RSpec.describe RakeJob do
+  let(:task_string) { "ofn:data:remove_transient_data" }
+
+  it "calls the removal service" do
+    expect(RemoveTransientData).to receive(:new).and_call_original
+    RakeJob.perform_now(task_string)
+  end
+
+  it "can be called several times" do
+    expect(RemoveTransientData).to receive(:new).twice.and_call_original
+    RakeJob.perform_now(task_string)
+    RakeJob.perform_now(task_string)
+  end
+end