feat: add fast multi-platform build

[merklefruit]

This PR adds support for building cross-platform binaries for x86_64 and aarch64 (unknown-linux-gnu).
We use cargo cross to produce a separate release binary for each architecture and successively load it
into a docker image directly.

Benefits:

• builds are fast, the part that takes longer is the linking at the end.
• no Docker overhead for build contexts, meaning also no need for janky docker cache layers
• lightweight output images, because we only ship the binary inside them

Downsides:

• since the images only contain the binary, it's harder to verify that they are running the correct binary. This is not a big issue because anyone wanting to verify their image integrity can build it locally from source.

Usage

Available packages that can be built from this repo (so far): bolt-sidecar, bolt-boost.

Example to produce a cross-platform image with tag unstable:

just build-and-push-image bolt-sidecar unstable

Example to produce cross-platform images for all available packages mentioned above with tag unstable:

just build-and-push-all-images unstable

Requisites to build images

• cargo
• cross
• docker buildx

[thedevbirb]

Awesome, super happy we got it working with the binary-based approach

[merklefruit]

Converted to draft because there is an openssl issue when building bolt-boost for aarch64

[merklefruit]

I had to remove the ssz-rs sha2-asm feature as it was breaking for cross-compiled aarch64.
There might be a way to do it but for now I had to disable it

[merklefruit]

Images tagged v0.3.0-alpha have been produced from the latest commit.

[thedevbirb]

🫡