Add ignore_empty Parameter to has_changed Method

[Mng-dev-ai]

Problem

The has_changed method returns True if the value changes from null to "" and vice versa, which is often not what we want

Solution

Added ignore_empty parameter with default value to True to ignore if value changed from null to "" and vice versa

Tests

I will add tests if you agree on the idea of this pr

[foarsitter]

Can you describe a use-case where None to empty string shouldn't be an actual change?

To me this sounds a little as https://docs.astral.sh/ruff/rules/django-nullable-model-string-field/