scripts/sbom: collect file metadata

scripts/sbom: collect file metadata

Implement the kernel_file module that collects file metadata,
including license identifier for source files, SHA-256 hash,
Git blob object ID, an estimation of the file type, and
whether files belong to the source, build, or output SBOM.

Assisted-by: Cursor:claude-sonnet-4-5
Assisted-by: OpenCode:GLM-4-7
Co-developed-by: Maximilian Huber <maximilian.huber@tngtech.com>
Signed-off-by: Maximilian Huber <maximilian.huber@tngtech.com>
Signed-off-by: Luis Augenstein <luis.augenstein@tngtech.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>