Return_attachment_instance_on_save_if_already_persisted

[ndianabasi]

Proposed changes

This PR instance the save method of the ResponsiveAttachment class to return the instance of the class if the instance is local or already persisted. This ensures that the column which the attachment is assigned to is not undefined.

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

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