Image layer code should inspect bytes instead of relying on file extension

[puerco]

What happened:

When extracting image layers, the layer analyzer will treat the blobs as a tar file or as compressed data depending on the file extension. This causes an error when the blobs are extracted and opened for inspection

What you expected to happen:

Layer blobs should be opened and inspected

How to reproduce it (as minimally and precisely as possible):

Trying to generate an SBOM with bom v0.2.0 of this Istio image fails:

wget https://storage.googleapis.com/istio-prerelease/prerelease/1.13.0-beta.0/docker/app-debug.tar.gz
bom generate --image-archive app-debug.tar.gz

INFO Generating SPDX Bill of Materials            
INFO Processing tarball app-debug.tar.gz          
INFO Generating SPDX package from image tarball app-debug.tar.gz 
INFO Successfully extracted 12 files from image tarball app-debug.tar.gz 
INFO Package describes istio/app:1.13.0-beta.0-debug image 
INFO Image manifest lists 7 layers                
FATA generating doc: creating SPDX document: generating tarball package: getting os data from container: reading os type from layer: reading os release: extracting os-release from tar: reading tarfile: archive/tar: invalid tar header 

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