Bring back listing LDAP users temporarly (#14760)

In previous releases, mc admin user list would return the list of users
that have policies mapped in IAM database. However, this was removed but
this commit will bring it back until we revamp this.

cmd/iam-store.go

@@ -1184,6 +1184,18 @@ func (store *IAMStoreSys) GetUsers() map[string]madmin.UserInfo {
 	return result
 }
 
+// GetUsersWithMappedPolicies - safely returns the name of access keys with associated policies
+func (store *IAMStoreSys) GetUsersWithMappedPolicies() map[string]string {
+	cache := store.rlock()
+	defer store.runlock()
+
+	result := make(map[string]string)
+	for k, v := range cache.iamUserPolicyMap {
+		result[k] = v.Policies
+	}
+	return result
+}
+
 // GetUserInfo - get info on a user.
 func (store *IAMStoreSys) GetUserInfo(name string) (u madmin.UserInfo, err error) {
 	if name == "" {