fix: Add support for generated enums in mutation input

[cngai]

Description

If GENERATE_ENUMS_FROM_CHOICES is set to True, mutations with enum input values will resolve the input type as an enum. When the input is parsed, it tries to save the field as an enum instead of a string value, causing Django to throw a ValidationError "Value 'ExampleEnum.VALUE' is not a valid choice.". This PR addresses this issue by parsing the enum and returning the enum value.

Types of Changes

• [ ] Core
• [x] Bugfix
• [ ] New feature
• [ ] Enhancement/optimization
• [ ] Documentation

Issues Fixed or Closed by This PR

Fix https://github.com/strawberry-graphql/strawberry-django/issues/491

Checklist

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[cngai]

Hey @bellini666 - would you mind giving this PR a review when you get the chance? Really appreciate it!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 87.98%. Comparing base (23c4126) to head (f624d12).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #497 +/- ## ========================================== + Coverage 87.97% 87.98% +0.01% ========================================== Files 37 37 Lines 3184 3187 +3 ========================================== + Hits 2801 2804 +3 Misses 383 383 ```

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[cngai]

Thanks @bellini666 !!