<!--- 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 -->

ishash = False
    if len(password) == 41 and password[0] == '*':
        if frozenset(password[1:]).issubset(string.hexdigits):
            ishash = True
    return ishash
def user_mod(cursor, user, host, host_all, password, encrypted,
             plugin, plugin_hash_string, plugin_auth_string, new_priv, append_privs, module):
    changed = False
    msg = "User unchanged"
    grant_option = False
    if host_all:
        hostnames = user_get_hostnames(cursor, [user])
    else:
        hostnames = [host]
    for host in hostnames:
        
        if bool(password):
            
            old_user_mgmt = use_old_user_mgmt(cursor)
            
            cursor.execute("""