Move hashing setting to its own section

Author: jkakavas

docs/reference/settings/security-settings.asciidoc

@@ -52,6 +52,8 @@ sensitive nature of the information.
 `xpack.security.authc.accept_default_password`::
 In `elasticsearch.yml`, set this to `false` to disable support for the default "changeme" password.
 
+[[password-hashing-settings]]
+==== Password hashing settings
 `xpack.security.authc.password_hashing.algorithm`::
 Specifies the hashing algorithm that is used for secure user credential storage
 (see {xpack-ref}/password-hashing.html#password-hashing-algorithms[Password hashing algorithms] table for all possible values). Defaults to `bcrypt`.