server cannot load client plugins on Debian

The problem is that client plugins are installed into /usr/lib/${DEB_HOST_MULTIARCH}/libmariadb3/plugin while server expects all plugins (server and client) to be in /usr/lib/mysql/plugin.

A simple solution that doesn't require moving any plugins anywhere and keeps server ownership of /usr/lib/mysql/plugin would be to symlink client plugins into /usr/lib/mysql/plugin.

Otto commented on this approach:

Indeed, symbolic links should be fairly backwards compatible and safe
to introduce. I can't come up with any downsides immediately.

I tested that now in
https://salsa.debian.org/mariadb-team/mariadb-server/-/merge_requests/94
but it would be better if those symbolic links were generated by CMake
in a uniform way to all platforms, and the Debian packaging only
needed to include existing files instead of generating them.