Fix Typo In LDAP Configuration Docs (quay#1268)

Starting with Quay 3.12 there was a new configuration option added
called LDAP_GLOBAL_READONLY_SUPERUSER_FILTER. When the documentation for
this feature was originally written(d2ab030)
it was incorrectly called GLOBAL_READONLY_SUPER_USERS.

Initial feature added to Quay here quay/quay#2917. Reference to code in latest commit on redhat-3.12 branch
https://github.com/quay/quay/blob/2c4c7570513b6dd205f7ce53ec25716baac45d85/data/users/__init__.py#L72-L74.

ref: https://issues.redhat.com/browse/PROJQUAY-7044

Author: seanmalloy

modules/config-fields-ldap.adoc

@@ -40,7 +40,7 @@ With this field, administrators can add or remove superusers without having to u
 
 This field requires that your `AUTHENTICATION_TYPE` is set to `LDAP`. 
 
-| **GLOBAL_READONLY_SUPER_USERS** | String | When set, grants users of this list read access to all repositories, regardless of whether they are public repositories. Only works for those superusers defined with the `LDAP_SUPERUSER_FILTER` configuration field.
+| **LDAP_GLOBAL_READONLY_SUPERUSER_FILTER** | String | When set, grants users of this list read access to all repositories, regardless of whether they are public repositories. Only works for those superusers defined with the `LDAP_SUPERUSER_FILTER` configuration field.
 
 | **LDAP_RESTRICTED_USER_FILTER** | String | Subset of the `LDAP_USER_FILTER` configuration field. When configured, allows {productname} administrators the ability to configure Lightweight Directory Access Protocol (LDAP) users as restricted users when {productname} uses LDAP as its authentication provider.
 
@@ -169,4 +169,4 @@ LDAP_USER_RDN:
     - dc=com
 # ...
 ----
-<1> Configures specified users as superusers.
+<1> Configures specified users as superusers.