[framework] getting position for new image is now more robust

[vitek-rostislav]

Description, the reason for the PR

The image count might not always be the highest position, e.g. when an image is removed, and positions are not recalculated.

Fixes issues

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Check the appropriate checkboxes below, please

• [x] BC breaks
• [ ] New feature
• [x] I have read and signed License Agreement for contributions

Summary by CodeRabbit

• New Features

  • Enhanced image upload functionality to determine the position of new images more effectively.
  • Introduced a method to retrieve the latest image position associated with entities.

• Documentation

  • Added upgrade notes to inform developers about the renaming of the image position retrieval method.

• Bug Fixes

  • Improved logic for determining image positions, ensuring more accurate results when uploading new images.

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• https://rv-images-position.odin.shopsys.cloud
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