core: crypto add support for SHA-512/256 for RFCs 8760/7616

[space88man]

Pre-Submission Checklist

• Commit message has the format required by CONTRIBUTING guide
• Commits are split per component (core, individual modules, libs, utils, ...)
• Each component has a single commit (if not, squash them into one commit)
• No commits to README files for modules (changes must be done to docbook files
  in doc/ subfolder, the README file is autogenerated)

Type Of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)

Checklist:

• PR should be backported to stable branches
• Tested changes locally
• Related to issue #XXXX (replace XXXX with an open issue number)

Description

This adds core/ support for SHA-512/256.

This is required for adding the SHA-512/256(“SHA-512-256”) digest algorithm to the auth module.

References:

• RFC8760
• RFC7616 and errata — the example given in RFC7616 for SHA-512-256 is incorrect (it truncated SHA-512 to 64 bytes instead of using the correct implementation of SHA-512/256 which has a different set of initial hash values)
• SHA-512/256 initial hash values