[TF-A] Welcoming Yann Gautier as a new TF-A maintainer!

Hi,

I am pleased to announce that Yann Gautier has now become one of the maintainers for TF-A. This decision is based on Yann's continued efforts and involvement in the project over the years.

A patch is under review to reflect this in TF-A documentation: https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/21060

Best regards, Sandrine (on behalf of all TF-A maintainers)