refactor: run crontab under sudo to support rhel systems

RHEL blocks users from executing crontab as themselves Because Of Reasons so we need to use sudo instead.

Also refactors file writing to properly support writing the permissions on sudoers files going forward.

Closes #5020

tests/unit/cron.bats

@@ -37,6 +37,13 @@ teardown() {
   assert_output "$help_output"
 }
 
+@test "(cron) installed" {
+  run /bin/bash -c "test -f /etc/sudoers.d/dokku-cron"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+}
+
 @test "(cron) invalid [missing-keys]" {
   run deploy_app python dokku@dokku.me:$TEST_APP template_cron_file_invalid
   echo "output: $output"