feat: add multiarch build

[kalidax]

This job will

• Build and push an image to dockerhub.
• Build tofnd binary, gpg sign it, zip it, create sha256 hashes for both zip and binary, upload files to release and S3.
• For binary build the job will run on each combination of OS/arch defined in the matrix.
• For the container build it will run one time only on ubuntu-18.04/amd64

Tests have been done here : https://github.com/axelarnetwork/tofnd/actions/workflows/matrix-build.yaml

[kalidax]

I close the PR, I need to add a working directory for tofnd, it will be more clean. I reopen one once done.