Add missing migration for webhooks

[zhiltsov-max]

Motivation and context

It seems that a migration was done in #4863 , but it was not added to the repository. This PR adds the missing migration, which is generated by python manage.py makemigrations.

• Changed the webhook model status_code field type

How has this been tested?

Checklist

• I submit my changes into the develop branch
• I have added a description of my changes into CHANGELOG file
• I have updated the documentation accordingly
• I have added tests to cover my changes
• I have linked related issues (read github docs)
• I have increased versions of npm packages if it is necessary (cvat-canvas,
  cvat-core, cvat-data and cvat-ui)

License

• I submit my code changes under the same MIT License that covers the project.
  Feel free to contact the maintainers if that's a concern.

[sizov-kirill]

Added migration quite similar with this migration.

And the reason why the lists of available values differ is because of the version of Python being used. Because for different python version http.HTTPStatus can differ.

So I think we should make WebhookDelivery.status_code independent from Python version.

And for now I see only one way to do it: hardcode all possible status codes. @zhiltsov-max what do you think about it?

[zhiltsov-max]

I think we can just store an integer without extra restrictions.

[nmanovic]

/check

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[zhiltsov-max]

/check

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