Catalog VM images directly

(writing on the behalf of @westonsteimel )

It would be awesome to be able to point syft directly and more filesystem image types:

```
# search a VMDK disk image
syft ./my.vmdk

# fetch and catalog from an EBS snapshot
syft ami-0abcdef1234567890
```

_(these would also have their own schemes too, such as `vmdk` and `eds`)_

There are some interesting libs available for accessing [EBS images](https://github.com/masahiro331/go-ebs-file), parsing [ext4 filesystems](https://github.com/masahiro331/go-ext4-filesystem), as well as [xfs filesystems](https://github.com/masahiro331/go-xfs-filesystem).

Ideally we could use the existing stereoscope filetree/index capabilities but have custom syft `Source` objects to raise specific metadata about that source.

Start by reviewing Syft's existing stereoscope filetree/index capabilities and Source objects. Investigate the linked EBS, ext4, and XFS libraries to determine how VMDK files and EBS snapshots could be accessed. Done means Syft can accept the proposed image inputs and expose source-specific metadata while cataloging their filesystems.

Written by the indexing model from the issue text.