LDAP: Fetch attributes in Bind DN context option

This is feature is workaround for #2628 (JumpCloud) and some other services
that allow LDAP search only under BindDN user account, but not allow any LDAP
search query in logged user DN context.

Such approach is an alternative to minimal permissions security pattern for
BindDN user.

modules/auth/auth_form.go

@@ -23,6 +23,7 @@ type AuthenticationForm struct {
 	AttributeName     string
 	AttributeSurname  string
 	AttributeMail     string
+	AttributesInBind  bool
 	Filter            string
 	AdminFilter       string
 	IsActive          bool