Provide official Windows ARM64 (aarch64) server binaries on the download page

Windows-on-ARM64 build support was contributed in https://github.com/MariaDB/server/pull/4060 and merged. However mariadb.org/download only offers x86_64 MSI/ZIP for Windows, so there is no way for users on Windows ARM64 devices (Snapdragon X series) to obtain a working server without building from source.

Ask: is adding an ARM64 Windows target to the release build matrix in scope? If the blocker is buildbot capacity / no ARM64 Windows worker, please say so — I have a native Windows ARM64 machine (Snapdragon X2 Elite) and can help with build verification or smoke-testing release candidates.