<!--- Verify first that your feature was not already discussed on GitHub -->
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##### 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 -->

cursor.execute("SELECT CONCAT('*', UCASE(SHA1(UNHEX(SHA1(%s)))))", (password,))
                encrypted_password = cursor.fetchone()[0]
            if current_pass_hash != encrypted_password:
                msg = "Password updated"
                if module.check_mode:
                    return (True, msg)
                if old_user_mgmt:
                    cursor.execute("SET PASSWORD FOR %s@%s = %s", (user, host, encrypted_password))
                    msg = "Password updated (old style)"
                else:
                    try:
                        cursor.execute("ALTER USER %s@%s IDENTIFIED WITH mysql_native_password AS %s", (user, host, encrypted_password))
                        msg = "Password updated (new style)"
                    except (mysql_driver.Error) as e:
                        
                        
                        if e.args[0] == 1396:
                            cursor.execute(
                                "UPDATE user SET plugin = %s, authentication_string = %s, Password = '' WHERE User = %s AND Host = %s",
                                ('mysql_native_password', encrypted_password, user, host)
                            )
                            cursor.execute("FLUSH PRIVILEGES")
                            msg = "Password forced update"
                        else:
                            raise e
                changed = True
        
        if plugin:
            cursor.execute("SELECT plugin, authentication_string FROM mysql.user "
                           "WHERE user = %s AND host = %s", (user, host))