refactor: rewriting some e2e tests

[EduardoJM]

The fundamental of this PR is:

1. We have some things: ArrayField widget and Inlines that works exactly same and we have a lot of duplicated test code.
2. We have the widget with various common things with ArrayField widget and Inline that have a lot of duplicated test code too.

The concept of this refactor is:

1. Create some test helper and mixins classes to run some common test-case's for each of this.
2. Make various tests inside a one test function to reduce the quantity of new browser/page opened.
3. Fix the broken UI Regression tests.
4. Fix any found behaviour mistake.
5. Turn the test code more semantic and readable.

Relation to the Issues:
closes #208
closes #207

Other informations:

Due we droped support for Django 3.x and we are rewriting tests, the broken UI regression tests are a real problem, we can merge #206 PR to closes #211 issue.