Updated LDAP docs (#939)

Update the AD/LDAP configuration instructions, including adding details
about configuring with Console.

Includes reformatting some existing content.

Questions:
- What, exactly, is the status of the `mc admin config identity_ldap`
settings? Deprecated? There, but not recommended for new configurations?
- Are the "all settings" examples correct and appropriate? I'm not clear
if `mc idp ldap` supports the same settings with the same names as
`identity_ldap`.

Staged:

http://192.241.195.202:9000/staging/DOCS-919/linux/html/operations/external-iam/configure-ad-ldap-external-identity-management.html

Fixes https://github.com/minio/docs/issues/919

---------

Co-authored-by: Ravind Kumar <ravind@min.io>
Co-authored-by: Daryl White <53910321+djwfyi@users.noreply.github.com>

source/administration/console/security-and-access.rst

@@ -145,6 +145,8 @@ Configuring an external IDP enables Single-Sign On workflows, where applications
 Use the the screens in this section to view, add, or edit OIDC configurations for the deployment.
 MinIO supports any number of active OIDC configurations.
 
+.. _minio-console-admin-identity-ldap:
+
 LDAP
 ~~~~
 
@@ -154,4 +156,5 @@ Configuring an external IDentity Provider (IDP) enables Single-Sign On (SSO) wor
 Use the the screens in this section to view, add, or edit an LDAP configuration for the deployment.
 MinIO only supports one active LDAP configuration.
 
-MinIO queries the active Active Directory / LDAP server to verify the credentials specified by the application and optionally return a list of groups in which the user has membership. 
+MinIO queries the Active Directory / LDAP server to verify the client-specified credentials. 
+MinIO also performs a group lookup on the AD/LDAP server if configured to do so.