Speed up beaker wasm build on Mac Silicon

[ethanfrey]

workspace-optimizer could be much faster. but we are using the amd64 type always:

Unable to find image 'cosmwasm/workspace-optimizer:0.12.6' locally
0.12.6: Pulling from cosmwasm/workspace-optimizer
...
Status: Downloaded newer image for cosmwasm/workspace-optimizer:0.12.6
WARNING: The requested image's platform (linux/amd64) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested

beaker could detect the local architecture and select between workspace-optimizer and https://hub.docker.com/r/cosmwasm/workspace-optimizer-arm64/tags. Alternately, we would be happy for a PR to build multi-architecture docker images, but that requires some other tooling, like CosmWasm/optimizer#67 first

[ethanfrey]

Never mind. After writing this, I found the -a option... https://github.com/osmosis-labs/beaker/blob/main/docs/commands/beaker_wasm.md#beaker-wasm-build