Package releases for arm64 on Ubuntu 20.04 and 22.04

[nhandyal]

Can we add an arm64 release of sapling? I currently have an ubuntu server running on an ARM processor and have to build sapling from source when configuring the server. It'd be great if this were available as an official package.

[daranday]

It seems 2 things need to happen:

1. building arm64 images
2. running arm64 containers to build debs

For 1), it's straight forward, I just added it in PR 933

For 2), it takes a little more effort, there are a couple of ways:

• run on Github's larger arm64 runners (in beta for org, needs admin configuration, perhaps @quark-zju knows more?)
• run on Github's free public arm64 runners (not yet available, could be a couple months)
• run with Qemu emulation, this looks promising: Run-on-arch

[quark-zju]

I'm not an expert in this area but I'll try to have a look when I got time.