Run Grype scan of files given from text file containing filelist

[tellmemoreaboutit]

What would you like to be added:
Run Grype scan of files given from text file containing file list.

Why is this needed:
When Grype is executed, it scans the pointed directory. However, it would be very useful if Grype has some functionality to scan only files specified in a text file.

Additional context:
Like "grype -i files-to-scan.txt"

files-to-scan.txt:
/etc/directory/file1.jar
/opt/directory/file2.jar
...
/var/directory/filex.jar

Also, JSON output, in this case, should contain an absolute path of the .artifact.locations[].path

[wagoodman]

This seems to highly related to anchore/syft#562 (we try to keep syft and grype aligned in how you express similar actions on the CLI, which is why I'm roping in a syft issue here), where we want to be able to specify multiple inputs (whether they are files, directories, images, etc), and not just a single input.

The current proposal is that this gets surfaced through the CLI as a list of arguments, so for grype:

grype ./path/to/file1 ./path/to/file2 ...

or by application configuration (TBD on final syntax):

input:
 - ./path/to/file1
 - ./path/to/file2

This would allow for more interesting configurations here too, such as mixing of source types:

grype docker:some/image:latest dir:/path/on/my/system file:./manifest.yaml

[kzantow]

An update: we started working on a way to support this, but ultimately have decided to put this on the back burner for the moment, as there are some blocking challenges. We will revisit this when the roadblocks are no longer impeding progress here.