Add command for regenerating pictures

[amureki]

Hey Johannes,

thanks again for the lib!

In my use case, I had my async worker failed several times due to the memory issues when migrating via AlterPictureField.
As a recovery solution, I was following the steps that are done in the migration and ran the following script on a bigger server premises:

for obj in MyModel.objects.exclude(image='').iterator():
    obj.image.update_all(
        from_aspect_ratios=PictureFieldFile.get_picture_files(
            file_name=obj.image.name,
            img_width=obj.image.width,
            img_height=obj.image.height,
            storage=obj.image.storage,
            field=obj.__class__._meta.get_field("image"),
        )
    )

I am proposing to add this as a management command to have a simpler way of recreating the thumbnails.
Here is a draft, happy to finalize it, rework if needed and add tests, but only if you accept it. :)

Best,
Rust

[codecov]

Codecov Report

Attention: 19 lines in your changes are missing coverage. Please review.

Comparison is base (33562b8) 100.00% compared to head (769bc50) 96.11%.
Report is 2 commits behind head on main.

Files	Patch %	Lines
...ictures/management/commands/regenerate_pictures.py	0.00%	19 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##              main     #153      +/-   ##
===========================================
- Coverage   100.00%   96.11%   -3.89%     
===========================================
  Files           13       14       +1     
  Lines          459      489      +30     
===========================================
+ Hits           459      470      +11     
- Misses           0       19      +19     

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[codingjoe]

@amureki you should check the migration implementation. You don't need to reinvent the wheel here. If said wheel, is a hypersphere ;)

[codingjoe]

Since I didn't see much activity here @amureki I will close this PR. Feel free to pick it up anytime.