AVIF images arenot automatically generated for existing images after enabling the option

[Mai-Saad]

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• Made sure you’re on the latest version => Avif commit: b396de2
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Describe the bug
When enabling AVIF, it isnot automatically generate AVIF for existing images in the media library

To Reproduce
Steps to reproduce the behavior:

1. Fresh activation of imagify
2. Upload a couple of images
3. Enable create AVIF option and save
4. Check FTP for images in 2 => AVIF not generated

Expected behavior
AVIF version is generated and quota is affected

Additional context
Add any other context about the problem here.

• related discussion https://wp-media.slack.com/archives/C069W48E47N/p1706878004622759?thread_ts=1706877044.964199&cid=C069W48E47N

Acceptance Criteria (for WP Media team use only)
Clear instructions for developers, to be added before the grooming

[Miraeld]

Umm, from my tests, here are some complementary informations:

• If we have the options Auto-Optimize images on upload but AVIF is disabled, when we upload images it gets optimized on upload, and get this status in the DB (wp_postmeta):

meta_key	meta_value
_imagify_status	already_optimized

Because of this, when we enable AVIF and save, it gets to this line where we get the unoptimized media_ids. However, as the status says already_optimized it won't return these images IDs.

• If we disable the options Auto-Optimize images on upload, upload images, and we enable AVIF and save, it will generate .avif files.

So the problems lies in the fact that Auto-Optimize images on upload set the status at already_optimized so images aren't getting picked up by the bulk optimization when we save with AVIF enabled.

[piotrbak]

@Miraeld Could you check how this button works in the current version? The behaviour should be very similar

[Miraeld]

I've compared a bit with develop branch.
From what I am seeing,

• When Auto-optimized is disabled, and we upload an image, we don't get the status already_optimized in the DB.
  It means we have a problem here with the AVIF branch.

@piotrbak I've tried to check the button, but it is also not working on avif branch, and I was trying to debug it on develop to see how it works, and why we could get an error, but once i clicked it one time it disappeared forever, even when I upload new images which aren't optimized. So not sure yet, I'm trying to figure out the differences between develop and avif on the upload part.

[Mai-Saad]

If we have single large image in media library then enabled AVIF, the AVIF won't be generated in background (tested local using attached image) @Miraeld can you please check if it's working for this image? (note: bulk notice wasnot displayed in this case)

[Miraeld]

@Mai-Saad , I've created this PR #811 to take care of this last feedback.