Docker image for arm

[joepio]

Current docker image is x86 only. I believe it's possible to use buildx to build a docker image compatible with arm.

[joepio]

I got buildx working just fine for linkux/arm64, but building the linux/arm/v7 image fails:

> [planner 3/5] RUN cargo install cargo-chef:                                                                                         
#13 1.278     Updating crates.io index                                                                                                 
#13 1.789 warning: spurious network error (2 tries remaining): could not read directory '/usr/local/cargo/registry/index/github.com-1285ae84e5963aae/.git//refs': Value too large for defined data type; class=Os (2)                                                         
#13 2.152 warning: spurious network error (1 tries remaining): could not read directory '/usr/local/cargo/registry/index/github.com-1285ae84e5963aae/.git//refs': Value too large for defined data type; class=Os (2)
#13 2.528 error: failed to fetch `https://github.com/rust-lang/crates.io-index`
#13 2.530 
#13 2.530 Caused by:
#13 2.531   could not read directory '/usr/local/cargo/registry/index/github.com-1285ae84e5963aae/.git//refs': Value too large for defined data type; class=Os (2)
------
dockerfile:9
--------------------
   7 |     FROM rust as cacher
   8 |     WORKDIR /app
   9 | >>> RUN cargo install cargo-chef
  10 |     COPY --from=planner /app/recipe.json recipe.json
  11 |     RUN cargo chef cook --release --recipe-path recipe.json
--------------------
error: failed to solve: rpc error: code = Unknown desc = executor failed running [/bin/sh -c cargo install cargo-chef]: exit code: 101

[joepio]

Issue being discussed here: docker/buildx#395