Expand on use of separate name attributes in LDAP

The `name` attribute in LDAP fetches the user's visible name in profiles
but often the ideal value for this is split between two different fields
that are configurable via  the use of `first_name` and `last_name`.

The docs were not very clear on how to force use of the latter (split)
configuration over `name`, doable by intentionally setting it to
something non-existent.

doc/administration/auth/ldap/index.md

@@ -201,9 +201,9 @@ LDAP attributes that GitLab uses to create an account for the LDAP user. The spe
 | ------- | ----------- | -------- | -------- |
 | `username` | The username is used in paths for the user's own projects (like `gitlab.example.com/username/project`) and when mentioning them in issues, merge request and comments (like `@username`). If the attribute specified for `username` contains an email address, the GitLab username is part of the email address before the `@`. | no | `['uid', 'userid', 'sAMAccountName']` |
 | `email` | LDAP attribute for user email. | no | `['mail', 'email', 'userPrincipalName']` |
-| `name` | LDAP attribute for user display name. If no full name could be found at the attribute specified for `name`, the full name is determined using the attributes specified for `first_name` and `last_name`. | no | `'cn'` or `'displayName'` |
-| `first_name` | LDAP attribute for user first name. | no | `'givenName'` |
-| `last_name` | LDAP attribute for user last name. | no | `'sn'` |
+| `name` | LDAP attribute for user display name. If `name` is blank, the full name is taken from the `first_name` and `last_name`. | no | Attributes `'cn'`, or `'displayName'` commonly carry full names. Alternatively, you can force the use of `first_name` and `last_name` by specifying an absent attribute such as `'somethingNonExistent'`. |
+| `first_name` | LDAP attribute for user first name. Used when the attribute configured for `name` does not exist. | no | `'givenName'` |
+| `last_name` | LDAP attribute for user last name. Used when the attribute configured for `name` does not exist. | no | `'sn'` |
 
 ### LDAP Sync Configuration Settings **(STARTER ONLY)**