Add Support for Automatic OS Detection in Packer Builders

Packer currently requires users to manually specify several OS-related configuration values such as distribution type, version, architecture, and boot commands, which can be complex and error-prone—especially when working with multiple templates or different Linux distributions. I would like to request a new feature that enables Packer to automatically detect the operating system and version from the provided ISO or boot image, and then apply the appropriate defaults for boot commands and provisioning options. This would simplify template creation, reduce user mistakes, improve build reliability, and make Packer more user-friendly by eliminating the need for lengthy manual boot command definitions.

No files, tests, or entry points are mentioned. Before implementation, clarify the supported distributions, detection signals, fallback behavior, and expected boot-command and provisioning defaults with maintainers; done should include agreed behavior and tests covering the supported cases.

Written by the indexing model from the issue text.