Promote kylejuliandev to dotnet-maintainers

[askpt]

This pull request moves kylejuliandev from the list of approvers to the list of maintainers.

Notes

@kylejuliandev contributes very actively to the dotnet-sdk and dotnet-contrib-sdk. He being helping the project for a while and I believe he is a great asset to the project. For the last couple of months, his contributions were:

• Improvements and adding extra functionality to the DI library
• Cleanup of the flagd provider and contrib repository in general
• Always reviewing all the open-feature related pull requests (even outside this organisation)
• Always available to discuss and bring innovation to the dotnet library
• https://github.com/open-feature/dotnet-sdk/commits/main/?author=kylejuliandev
• https://github.com/open-feature/dotnet-sdk-contrib/commits/main/?author=kylejuliandev

@kylejuliandev, please approve this PR or +1 if you accept this nomination!