feat: add endpoint to update testimonials for authenticated users

[edenis00]

Description

This PR adds an endpoint that allows authenticated users to update their testimonials. It ensures users can modify their previously submitted feedback while maintaining data integrity.

Related Issue (Link to issue ticket)

#1154

Motivation and Context

This change is required to enable users to update their testimonials, allowing them to correct errors or modify their feedback over time. It enhances the user experience by ensuring testimonials remain relevant and accurate.

How Has This Been Tested?

This feature has been tested using:

• Unit tests with FastAPI’s TestClient and pytest
• Mocking database queries to simulate different scenarios (successful update, unauthorized access, and non-existent testimonial)
• Manual testing using Postman, sending requests with different authentication states
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Screenshots (if appropriate - Postman, etc):

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Types of changes

• Bug fix (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 change)
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Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.