Build and push Linux riscv64 images

[olof-nord]

I wanted to use the AppImageKit on a Linux risc-v machine.

When trying to build it, I noticed that there were no riscv64 images available.

As since Ubuntu is publishing riscv64 images, here is a AppImageBuild riscv64 suggestion, built in the same way as the aarch64 and armhf build images.

The base image focal is chosen as there are no riscv64 base image for bionic.

RISC-V is an open standard instruction set architecture, which is under rapid development. Distributions including AOSP, Arch Linux, Debian, Gentoo Linux, Fedora, OpenEuler, etc are also actively doing porting work for this architecture.

Here is a list of hardware available today: https://riscv.org/exchanges/boards/

I run and own a SiFive Unmatched.

[TheAssassin]

Pull request did not trigger. I re-enabled the workflow. You should squash your two commits anyway, so we could use this push to generate a new build.

[olof-nord]

Commits are squashed, however to try out the Workflow, I need an approval:

This workflow is awaiting approval from a maintainer

[olof-nord]

Just a small comment on this - RISC-V is here to stay and I think the recent developments around new hardware is a testament to this. Do you support adding a new platform @TheAssassin ? If yes, what is left on this PR?