Add Argon2PasswordEncoder

[simmac]

Add PasswordEncoder for the Argon2 hashing algorithm (Password Hashing
Competition (PHC) winner).
This implementation uses the BouncyCastle-implementation of Argon2.

Fixes gh-5354

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[rwinch]

Thanks for the PR @simmac! I have provided some minor comments inline.

[larsgrefer]

How about also implementing upgradeEncoding in the spirit of #7057 and #7042 ?

[simmac]

sorry for the delay.
I worked in all your feedback and implemented @larsgrefer's suggestion (thank you!) :)

[rwinch]

The code looks great now. One last request. Can you please add some documentation in https://github.com/spring-projects/spring-security/blob/c05b0765c1741eaaa237ed58cb72cd57385a173a/docs/manual/src/docs/asciidoc/_includes/servlet/architecture/password-encoder.adoc#bcryptpasswordencoder Please:

• place below bcrypt
• follow the same outline as bcrypt
• mention the password hashing competition
• mention that it requires bouncy castle.

[simmac]

Done @rwinch, hope this is sufficient

[rwinch]

Thanks for all your hard work on this @simmac! This is now in master

[relsayed8205]

Hi,
I have a small question:
Why is the BouncyCastle dependency not added to the maven central repository by default? One have to state it explicitly in their pom.xml, which seems strange, as using maven should automate retrieving all dependencies.
Thanks