Add userHash validation for the user import endpoint

[seluianova]

Is your feature request related to a problem? Please describe.
Follow up for #1433
Implement isValidUserHash() function in UserImportHandler

Describe the solution you'd like

• parse userHash string
• verify params:

$argon2id: means which algorithm is used
v=19: means which version is used
m=16 means which memory costs are used
t = 2 means which number of iterations are used
p = 1 means which numer of paralellis is used

We can probably re-use somethong from decode() function here:
https://github.com/spring-projects/spring-security/blob/main/crypto/src/main/java/org/springframework/security/crypto/argon2/Argon2EncodingUtils.java