This change adds documentation for the `realm` field to the Chinese (zh)
HMAC auth plugin documentation.

The content follows the existing English documentation and keeps the same
structure and meaning. No functional or code changes are included.

docs(zh): add realm field to ldap-auth plugin docs

This commit updates the Chinese documentation of the ldap-auth
plugin by adding information about the `realm` field.

The description explains how the realm value is included in the
WWW-Authenticate header when authentication fails, improving
clarity and keeping the zh documentation consistent with other
authentication plugin documentation.