Flip setting to delete finished jobs, to preserve them

And preserve them by default. Also, add a new option to indicate when
to delete preserved jobs.

app/models/solid_queue/job/executable.rb

@@ -29,10 +29,10 @@ def prepare_for_execution
       end
 
       def finished!
-        if delete_finished_jobs?
-          destroy!
-        else
+        if preserve_finished_jobs?
           touch(:finished_at)
+        else
+          destroy!
         end
       end
 
@@ -77,8 +77,8 @@ def ready
         end
 
 
-        def delete_finished_jobs?
-          SolidQueue.delete_finished_jobs
+        def preserve_finished_jobs?
+          SolidQueue.preserve_finished_jobs
         end
     end
   end

lib/solid_queue.rb

@@ -33,7 +33,8 @@ module SolidQueue
   mattr_accessor :supervisor_pidfile
   mattr_accessor :supervisor, default: false
 
-  mattr_accessor :delete_finished_jobs, default: true
+  mattr_accessor :preserve_finished_jobs, default: true
+  mattr_accessor :clear_finished_jobs_after, default: 1.day
   mattr_accessor :default_concurrency_control_period, default: 3.minutes
 
   def self.supervisor?

test/dummy/config/application.rb

@@ -28,6 +28,5 @@ class Application < Rails::Application
     # config.eager_load_paths << Rails.root.join("extras")
 
     config.active_job.queue_adapter = :solid_queue
-    config.solid_queue.delete_finished_jobs = false
   end
 end

test/integration/jobs_lifecycle_test.rb

@@ -66,9 +66,9 @@ class JobsLifecycleTest < ActiveSupport::TestCase
 
   private
     def deleting_finished_jobs
-      previous, SolidQueue.delete_finished_jobs = SolidQueue.delete_finished_jobs, true
+      previous, SolidQueue.preserve_finished_jobs = SolidQueue.preserve_finished_jobs, false
       yield
     ensure
-      SolidQueue.delete_finished_jobs = previous
+      SolidQueue.preserve_finished_jobs = previous
     end
 end