Build Linux ARM binaries in the CI

[jpraynaud]

Why

We want to provide pre-built binaries for Linux ARM in our GitHub releases.

This is a feature requested by the community (discord) and which follows-up with the issue #1751.

Important

Based on current usages of the CI, we evaluate that ~100,000 minutes will be needed for 12 months of a similar usage of the CI that we had for the last 12 months. We would need 5 ARM runners of type Linux 2-core or Linux 4-core.

What

Update the CI to create a Linux ARM binary for the aggregator, signer and clients.

How

• Allocate a Linux ARM runner to the Mithril repository
• Update the CI to use a Linux ARM runner
• Provide Docker images for ARM?