Add RISC-V support to project

[olof-nord]

Description

Adjust goreleaser config to add build and docker support.

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.

🚨 Before submitting your PR, please read community, and indicate which issues (in any of the repos) are either fixed or closed by this PR. See GitHub Help: Closing issues using keywords.

• DO make sure you are requesting to pull a topic/feature/bugfix branch (right side). Don't request your master!
• DO make sure you are making a pull request against the master branch (left side). Also you should start your branch off our master.
• DO make sure that File Browser can be successfully built. See builds and development.
• DO make sure that related issues are opened in other repositories. I.e., the frontend, caddy plugins or the web page need to be updated accordingly.
• AVOID breaking the continuous integration build.

Further comments

Add new arch-specific alpine Dockerfile as there is not yet any linux/riscv64 support for alpine:latest.
https://hub.docker.com/r/riscv64/alpine

I tried to look at how other architectures were set up: if there is any config missing just let me know and I will add it.

[github-actions]

This PR is stale because it has been open 30 days with no activity. Remove stale label or comment or this will be closed in 5 days.

[github-actions]

This PR was closed because it has been stalled for 5 days with no activity.

[olof-nord]

Well, if someone wants to add this in the future, feel free to take this branch as a starting point.

[olof-nord]

This process seems to be automatic - if it wasn't, it would be great to know what could have been done differently for suggesting changes and improvements to the project.