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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 -->

type: str
    default: localhost
  host_all:
    description:
      - Override the host option, making ansible apply changes to all hostnames for a given user.
      - This option cannot be used when creating users.
    type: bool
    default: no
    version_added: "2.1"
  priv:
    description:
      - "MySQL privileges string in the format: C(db.table:priv1,priv2)."
      - "Multiple privileges can be specified by separating each one using
        a forward slash: C(db.table:priv/db.table:priv)."
      - The format is based on MySQL C(GRANT) statement.
      - Database and table names can be quoted, MySQL-style.
      - If column privileges are used, the C(priv1,priv2) part must be
        exactly as returned by a C(SHOW GRANT) statement. If not followed,
        the module will always report changes. It includes grouping columns
        by permission (C(SELECT(col1,col2)) instead of C(SELECT(col1),SELECT(col2))).
      - Can be passed as a dictionary (see the examples).
    type: raw
  append_privs:
    description:
      - Append the privileges defined by priv to the existing ones for this
        user instead of overwriting existing ones.
    type: bool
    default: no
    version_added: "1.4"
  sql_log_bin: