Update password4j docs to use BcryptPassword4jPasswordEncoder

[nidhogg5]

Fix: Corrected class name inconsistency in password-storage.adoc example

[rwinch]

@nidhogg5 Thanks for the Pull Request! Can you please update the commit to include the Signed-Off-by trailer to all of your commit message to fix the DCO checks? You can read more about the move to using DCO on the Spring Blog.