add support for other filetypes for CAPE sandbox analysis

[williballenthin]

https://github.com/mandiant/capa/blob/151d30bec6f09f2a62420ad1ea18d51f5a5757ea/capa/features/extractors/cape/extractor.py#L136

We have access to a bunch of non-PE results internally, so at least we can develop and test locally. Ideally we find some public non-PE CAPE results that we can add to our capa-testfiles repository to prove the changes work (fyi @doomedraven)