Add relationships to ELF packages

[brian-ebarb]

This PR adds DependencyOf relationships when ELF packages have been discovered by the binary cataloger. The discovered file.Executable type has a []ImportedLibraries that's read from the file when discovered by syft. By mapping these imported libraries back to the package collection, syft is able to create relationships showing which packages are dependencies of other packages by just reading metadata from the ELF executable.

Testing

The integration test found under cmd/syft/internal/test/integration/package_binary_elf_relationships_test.go covers a sample image where the following graph is true:

"glibc": {
	"libhello_world.so",
	"syfttestfixture",
},
"libstdc++": {
	"syfttestfixture",
},
"libhello_world.so": {
	"syfttestfixture",
},

The above data structure can be read as glibc IS A DEPENDENCY OF syfttestfixture

For more information about the fixture see this document:
https://github.com/anchore/syft/blob/4fe0c98d0fe85417be596836d8798b7b10d43b1f/syft/pkg/cataloger/binary/test-fixtures/elf-test-fixtures/README.md

[spiffcs]

I've updated the unit tests and SA on this PR - there are maybe 2 more cases to cover, but we're very close.

The one issue in particular I'm keen on testing is if the relationships are still created IF an RPM package shadows/overrides an ELF binary package. We need a way to pass the import paths discovered up to the RPM package so that these don't get dropped

[spiffcs]

From my perspective there is one final TODO on this PR:

A case needs to be covered where syft does some clean up during Finalize and removes duplicate packages (this code has not yet been written).

Example: if ELF Package (a) is a part of RPM Package (b), then ELF Package (a) is deleted as a duplicate from the SBOM... this means that RPM Package (b) should all get all of ELF Package (A)s relationships.

I'm working on this now as the final addition.

If @wagoodman could look at the whole PR and give his final thoughts on if we're missing anything else that would be very much appreciated