feat(course-mentors): migrate to nestjs

[ThorsAngerVaNeT]

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🤔 This is a ...

• New feature
• Bug fix
• Performance optimization
• Refactoring
• Test Case
• Documentation update
• Other

🔗 Related issue link

#2255

💡 Background and solution

Migrate course/mentors endpoints from Koa to NestJS, update FE to new endpoint routes

☑️ Self Check before Merge

⚠️ Please check all items below before review. ⚠️

• Database migration is added or not needed
• Documentation is updated/provided or not needed
• Changes are tested locally

[apalchys]

@ThorsAngerVaNeT could you please update the branch with the latest changes to make sure CI passes?

[ThorsAngerVaNeT]

@ThorsAngerVaNeT could you please update the branch with the latest changes to make sure CI passes?

Sure