Follow-up of #5953.
Refactor the concerns with two goals:
- Getting closer from the way ActiveStorage adds its own hooks.
Usually ActiveStorage does this using an `Attachment#after_create`
hook, which then delegates to the blob to enqueue the job.
- Enqueuing each job only once. By hooking on `Attachment#after_create`,
we guarantee each job will be added only once.
We then let the jobs themselves check if they are relevant or not, and
retry or discard themselves if necessary.
We also need to update the tests a bit, because Rails'
`perform_enqueued_jobs(&block)` test helper doesn't honor the `retry_on`
clause of jobs. Instead it forwards the exception to the caller – which
makes the test fail.
Instead we use the inline version of `perform_enqueued_jobs()`, without
a block, which properly ignores errors catched by retry_on.
This warning re-appeared when running mailer tests:
```
DISABLE_SPRING=1 bin/rspec spec/mailers/administration_mailer_spec.rb
```
It is now fixed properly, in a way recommanded by the documentation.
For some reason on Rails 6.1 the `after_update_commit` hook is properly
registered – but disappears from the record later, and in the end is
never run.
Fix it by using the general `after_commit` hook instead.
Fix a warning when running tests:
> DEPRECATION WARNING: Initialization autoloaded the constant DynamicSmtpSettingsInterceptor.
>
> Being able to do this is deprecated. Autoloading during initialization is going
to be an error condition in future versions of Rails.
>
> Reloading does not reboot the application, and therefore code executed during
> initialization does not run again. So, if you reload DynamicSmtpSettingsInterceptor, for example,
> the expected changes won't be reflected in that stale Class object.
>
> This autoloaded constant has been unloaded.
>
> Please, check the "Autoloading and Reloading Constants" guide for solutions.
However if we fix as recommanded, the interceptor will get added
each time the classes are reloaded. And as the actual class instance
changed after the reloading, they won't be de-duplicated – *and*
there's no way to remove the old interceptor without having a reference
to the (now-deleted) class.
Instead we load the interceptor once, and add a message about the class
not being auto-reloaded.
