Build for amd+arm with same tag

[shramee]

So docker can auto-select based on system.

[FabijanC]

You are aiming at the fact that arm images require the -arm suffix?

Supporting it without the suffix was the initial idea when we were introducing arm support, but was unable to achieve this. Do you have experience with this? Also it would be great if this could be achieved using CircleCI runners.

Cc: @LucasLvy

[shramee]

Yeah sure, I can have a look.

[shramee]

It's actually rather straightforward with docker cli, circleci should support that too.