DOCS: Add password_hash & refresh to Put User API (#35574)

PR #35242 formalised support for the password_hash field in the body
of the Put User security API.
Since this field is now validated and tested, it can also be
documented.

The Put User API also supports a "refresh" query parameter that was
not documented. This commit adds it to the docs.

x-pack/docs/en/rest-api/security/create-users.asciidoc

@@ -35,6 +35,12 @@ printable symbols in the https://en.wikipedia.org/wiki/Basic_Latin_(Unicode_bloc
 
 --
 
+==== Query Parameters
+
+`refresh`::
+    (string) One of `true`, `false`, or `wait_for`.
+    These values have the same meaning as in the <<docs-refresh, Index API>>,
+    but the default value for this API (Put User) is `true`.
 
 ==== Request Body
 
@@ -52,8 +58,26 @@ The following parameters can be specified in the body of a POST or PUT request:
 `metadata`::
 (object) Arbitrary metadata that you want to associate with the user.
 
-`password` (required)::
+`password` ::
 (string) The user's password. Passwords must be at least 6 characters long.
++
+When adding a user, one of `password` or `password_hash` is required.
+When updating an existing user, the password is optional, so that other
+fields on the user (such as their roles) may be updated without modifying
+the user's password.
+
+`password_hash` ::
+(string) A _hash_ of the user's password. This must be produced using the
+same hashing algorithm as has been configured for password storage. For more
+details, see the explanation of the
+`xpack.security.authc.password_hashing.algorithm` setting in
+<<hashing-settings>>.
++
+Using this parameter allows the client to pre-hash the password for
+performance and/or confidentiality reasons.
++
+The `password` parameter and the `password_hash` parameter cannot be
+used in the same request.
 
 `roles` (required)::
 (list) A set of roles the user has. The roles determine the user's access