Provide a warning if the package being added isn't the right architecture

[Justinzobel]

I've just been trying to work out why my package didn't show up even though it added fine and published.

This was because my published repository was set to arm64 + amd64 and I was pushing an armhf package.

It would be great if when adding or publishing aptly showed a warning saying that the package x doesn't match the architecture and won't be shown.