Support Argon2 as hashing algo in htpasswd

[filex]

Couper supports a htpasswd_file in the basic_auth access control.

There is already a range of hashing algorithms supported like APR1 style, bcrypt….

I would like to use argon2 as this seems to be the latest greatest way of hashing passwords.

Argon2 hashes use a similar prefix: $argon2id$ (or just i or d). so it would be simple to detect.

[filex]

we could use the x-package https://pkg.go.dev/golang.org/x/crypto/argon2.