<!--- Verify first that your feature was not already discussed on GitHub -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Describe the new feature/improvement briefly below -->
New Percona/MySQL 8 privileges with underscore is not working. 
the following error is coming 

`MSG: invalid privileges string: Invalid privileges specified: frozenset({'BACKUP_ADMIN'})`

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
mysql_user module
most likely the new privileges needs to be added to lib/ansible/modules/database/mysql/mysql_user.py

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml

```

<!--- HINT: You can also paste gist.github.com links for larger files -->

plugin, plugin_hash_string, plugin_auth_string,
                                            priv, append_privs, module)
                else:
                    changed, msg = user_mod(cursor, user, host, host_all, None, encrypted,
                                            plugin, plugin_hash_string, plugin_auth_string,
                                            priv, append_privs, module)
            except (SQLParseError, InvalidPrivsError, mysql_driver.Error) as e:
                module.fail_json(msg=to_native(e))
        else:
            if host_all:
                module.fail_json(msg="host_all parameter cannot be used when adding a user")
            try:
                changed = user_add(cursor, user, host, host_all, password, encrypted,
                                   plugin, plugin_hash_string, plugin_auth_string,
                                   priv, module.check_mode)
                if changed:
                    msg = "User added"
            except (SQLParseError, InvalidPrivsError, mysql_driver.Error) as e:
                module.fail_json(msg=to_native(e))
    elif state == "absent":
        if user_exists(cursor, user, host, host_all):
            changed = user_delete(cursor, user, host, host_all, module.check_mode)
            msg = "User deleted"
        else:
            changed = False
            msg = "User doesn't exist"
    module.exit_json(changed=changed, user=user, msg=msg)
if __name__ == '__main__':
    main()