fix: FormFillerTextIT related to model changes, and some imports cleanup.

[czp13]

Description

Fixes and changes in the FormFillerTextIT related to the model change (deprecated text-davinci-003 to gpt-3.5-turbo-instruct).

• The description is filled differently (not worse just a bit more verbose)
• also date fills maybe not as stable (as we have 2-3 dates in the text, it can choose randomly it seems)

Fixes # (issue)

• PiT 24.4: form description is filled incorrectly, making test fail #17

Type of change

• Bugfix
• Feature

Checklist

• I have read the contribution guide: https://vaadin.com/docs/latest/guide/contributing/overview/
• I have added a description following the guideline.
• The issue is created in the corresponding repository and I have referenced it.
• I have added tests to ensure my change is effective and works as intended.
• New and existing tests are passing locally with my change.
• I have performed self-review and corrected misspellings.

Additional for Feature type of change

• Enhancement / new feature was discussed in a corresponding GitHub issue and Acceptance Criteria were created.