Support several pqclean upstream versions

[baentsch]

Fixes #1584.

This PR should be completed/rebased once #1589 landed.

This adds the ability to reference different pqclean versions (commits); kyber-aarch64 and dilithium-aarch64 are pinned to a new upstream name "oldpqclean". True upgrades following more current versions/commits of PQClean should be added only to the "pqclean" upstream. The logic has been tested with #1585 and seems to work OK. The proposal is to land this PR, then rebase #1585 to it.

This PR also removes the unsupported "NOT_READY" feature from copy_from_upstream.

When this lands, an update to the documentation in the wiki is warranted/will be done.

• [no] Does this PR change the input/output behaviour of a cryptographic algorithm (i.e., does it change known answer test values)? (If so, a version bump will be required from x.y.z to x.(y+1).0.)
• [no] Does this PR change the list of algorithms available -- either adding, removing, or renaming? Does this PR otherwise change an API? (If so, PRs in fully supported downstream projects dependent on these, i.e., oqs-provider and OQS-OpenSSH will also need to be ready for review and merge by the time this is merged.)

[baentsch]

FWIW, latest commit is a rebase-and-squash (in case you'd like to check again @dstebila )

[SWilson4]

Looks good to me! I'm glad that it wasn't necessary to rewrite the entire copy_from_upstream script. Thanks @baentsch.

[baentsch]

I'm glad that it wasn't necessary to rewrite the entire copy_from_upstream script.

I'm not sure about that. This script is pretty hard to understand and maintain and a re-write might be (more) beneficial in the long run.