Add PBKDF2 as password hashing algorithm

[sawadashota]

Is your feature request related to a problem? Please describe.

I want to choose PBKDF2 as password hashing algorithm.
I'm planning to migrate ID system to kratos but a password hashing algorithm in my system is PBKDF2 (This is Django Default).

According to kratos overview, we can choose many algorithms but currently we can choose only argon2 or bcrypt.
https://www.ory.sh/kratos/docs/concepts/index/#roll-your-own
https://www.ory.sh/kratos/docs/reference/configuration/

If kratos adds PBKDF2 as password hashing algorithm, I can migrate ID system with less user pain.

Describe the solution you'd like

Add PBKDF2 hasher
https://github.com/ory/kratos/tree/master/hash

Describe alternatives you've considered

Additional context

[aeneasr]

Adding PKBDF2 as a n password import option is definitely an option!