Async bulk optimization

[remyperona]

What are we proposing to do?

With this update, we want to make the Bulk Optimization asynchronous.

Why are we doing this?

We want to improve the user experience with the Bulk Optimization to make it faster and easer to use.

The current solution is not efficient for two reasons:

1. The process can't run in the background (tab should be open). For websites with a ton of images, users have to stay on the page for a while (sometimes days!). Our users want to start it and "forget" about it until it's done.
2. It can't be triggered via cron programmatically. If a user would like to automatically run the bulk optimization with a script, it’s not possible. A manual action is needed, and we came back to the problem of the need to stay on the page.

https://docs.google.com/document/d/1DBakkW4zVEeeh2GDv8wYYTdyKVcQAW0VT44Z9FQRkv4/edit?usp=sharing