dossiers: unify deletion of dossiers between manager and user

The code paths for deleting a dossier were different, depending on
whether the dossier was deleted by the user, or from the Manager.

This commit unifies the two code paths into one.

This has the effect of:

- An operation log is now recorded when an user deletes its own dossier;
- Gestionnaires are now notified even when the dossier is deleted from
  the Manager;
- The `support:delete_user_account` task now requires the email address
  of the author.

lib/tasks/support.rake

@@ -2,19 +2,26 @@ require Rails.root.join("lib", "tasks", "task_helper")
 
 namespace :support do
   desc <<~EOD
-    Delete the user account for a given USER_EMAIL.
+    Delete the user account for a given USER_EMAIL on the behalf of ADMIN_EMAIL.
     Only works if the user has no dossier where the instruction has started.
   EOD
   task delete_user_account: :environment do
     user_email = ENV['USER_EMAIL']
-    if user_email.nil?
-      fail "Must specify a USER_EMAIL"
-    end
-    user = User.find_by(email: user_email)
+    fail "Must specify a USER_EMAIL" if user_email.nil?
+
+    administration_email = ENV['ADMIN_EMAIL']
+    fail "Must specify the ADMIN_EMAIL of the operator performing the deletion (yourself)" if administration_email.nil?
+
+    user = User.find_by!(email: user_email)
+    administration = Administration.find_by!(email: administration_email)
+
     if user.dossiers.state_instruction_commencee.any?
       fail "Cannot delete this user because instruction has started for some dossiers"
     end
-    user.dossiers.each(&:delete_and_keep_track)
+
+    user.dossiers.each do |dossier|
+      dossier.delete_and_keep_track(administration)
+    end
     user.destroy
   end