Replacing ldap_user_enabled_default type from boolean to string

Change-Id: Ib2ee5c0c16573e70eb212fde66588ee88991e2c6
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>

installers/charm/keystone/config.yaml

@@ -185,7 +185,7 @@ options:
       user is enabled.
     default: 0
   ldap_user_enabled_default:
-    type: boolean
+    type: string
     description: |
       Most LDAP servers use a boolean or bit in a control field to indicate
       enablement. However, some schemas might use an integer value in an