Ensure pkam verb handler accepts SHA512 as a valid hashing algorithm

[srieteja]

Describe the bug

Although AtChops has logic to sign and verify data using SHA512, PKAM verb does not recognize SHA512 as a valid hashing algo. After debugging, turns out that this is due to the regex explicitly accepting only SHA256.

Steps to reproduce

1. Create an OnboardingCli instance with hashing algo set to SHA512 in AtOnboardingPreference and other required preferences set
2. Call onboardingService.authenticate()
3. This will trigger a format exception

Expected behavior

Signing and verification should be performed seamlessly when using SHA256 or SHA512

[srieteja]

This issue has been fixed by this PR: atsign-foundation/at_libraries#622