When Redis is configured to use an ACL file (with the `aclfile` configuration
option), this command will save the currently defined ACLs from the server
memory to the ACL file.

@return

@simple-string-reply: `OK` on success.

The command may fail with an error for several reasons: if the file cannot be
written or if the server is not configured to use an external ACL file.

@examples

```
> ACL SAVE
+OK

> ACL SAVE
-ERR There was an error trying to save the ACLs. Please check the server logs for more information
```