Improve signature verification in VM-Assert-Signature

[Ana06]

Details

The current implementation of VM-Assert-Signature uses Get-AuthenticodeSignature status. Reading Microsoft documentation, I understand that this only checks that the file has a syntactically syntactically valid signature, I think we should instead verify the signing authority, for example using signtool.exe:

"C:\Program Files (x86)\Windows Kits\10\bin\10.0.17763.0\x86\signtool.exe" verify /pa /all /tw /v /d googlechromestandaloneenterprise64.msi

This works well for Google Chrome, Sysinternals and Metasplot, but not for RegCool. I suggest using hashes again in RegCool. Should we also replace it in the configuration by total-registry to avoid that updates break the tool leaving FLARE-VM without a registry tool?

[Ana06]

It may also be possible to validate the signature of RegCool using signtool, but I am not sure how. Can someone help here? @mandiant/vms