Add support for multiple backup destination types using rclone

Key Changes

• Database & API

  • Extended the backup destination schema to include type (e.g., s3, gdrive, onedrive, ftp, sftp, webdav, etc.) and rcloneConfig (for rclone connection strings/configs).
  • Updated all relevant API endpoints and validation to support the new fields and logic.

• Frontend

  • Updated the destination creation/edit form:
    • Added a dropdown for destination type.
    • If S3 is selected, S3-specific fields are shown.
    • For other types, a textbox for rclone config/connection string is shown, with a link to rclone docs.
  • Improved UX for adding and editing backup destinations.

• Backup Logic

  • Unified backup upload logic for all providers using a new utility function.
  • All backup routines (Postgres, MySQL, MariaDB, Mongo, Compose, Web Server) now support any rclone-compatible provider.
  • Test connection logic supports both S3 and non-S3 types.

Closes- #416 /claim #416