Riscv64 becomes official Debian architecture

After many years of effort, I am happy to announce that Debian riscv64 is now an official architecture!

This milestone is not the end of the journey but rather the beginning of a new one: the port will need to be rebootstrapped in the official archive, build daemons will have to be reinstalled and handed over to DSA, many bugs will need to be fixed. If everything goes well, the architecture will eventually be released with Trixie. Please note that this process will be long and will span several months.

An important step in any architecture's life cycle is becoming an officially supported Debian architecture.