Cleanup and separate usage of os and arch that we conflate in our workflows

[tt-rkim]

from this discussion: #15523 (comment)

we aren't consistent with our os and arch variable usage in our workflows.

We should be explicit about these values, and not have things like ubuntu-20.04-amd64.

cc @blozano-tt @afuller-TT @ttmchiou

Setting this as P3 for now

[tt-rkim]

@dimitri-tenstorrent - Also relevant to your work. We haven't been as attentive to the tags, and this is something we should pick up after we merge in your releases image PR.