Add Database Backup Feature (Disabled by Default) and Use backup User for Multi-DB Support

[NUZAT-TABASSUM]

New features:

• The backup feature is disabled by default. To enable it, set database_backup_enabled: true and provide a value for database_backup_output_path.

• You can set the backup path, schedule, how many old backups to keep, file ownership, and more—all through variables.

• Dedicated backup user:
  Backups now use a dedicated backup database user with read-only privileges for the target databases (instead of root or an application user). This approach is safer, as it avoids using highly privileged accounts for automated operations. Also, the backup user is created automatically with the necessary permissions when backups are enabled.

• You can set the backup user’s password using the database_backup_user_password variable.

• Just list the databases you want to back up in the database_backup_dbs variable, for example:

 database_backup_dbs:
    - opencast
    - tobira
    - mycustomdb

[wsmirnow]

Good job overall, thank you @NUZAT-TABASSUM

There are some comments below, please take a look at it. Please add documentation of the new arguments in the README. And please add an DB restore script too.

[NUZAT-TABASSUM]

Hello @wsmirnow, I have updated the codes based on your comments, updated README and added a DB restore script. Please re-review.