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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 -->

description:
      - Whether binary logging should be enabled or disabled for the connection.
    type: bool
    default: yes
    version_added: "2.1"
  state:
    description:
      - Whether the user should exist.
      - When C(absent), removes the user.
    type: str
    choices: [ absent, present ]
    default: present
  check_implicit_admin:
    description:
      - Check if mysql allows login as root/nopassword before trying supplied credentials.
    type: bool
    default: no
    version_added: "1.3"
  update_password:
    description:
      - C(always) will update passwords if they differ.
      - C(on_create) will only set the password for newly created users.
    type: str
    choices: [ always, on_create ]
    default: always
    version_added: "2.0"
  plugin:
    description:
      - User's plugin to authenticate (``CREATE USER user IDENTIFIED WITH plugin``).
    type: str