patch rfc: debuginfod -Z (generalized archive) support

[Frank Ch. Eigler]

Hi - 

> I really like how simple adding this feature is. Shows the design for
> adding new formats was done with some foresight.

Thanks!

> [...] I think it would be better if you could simply leave off the
> conversion CMD and just provide an EXT (without =). This would then
> just pass the file with the given extension to libarchive directly
> (then you also don't need the zstdcat conversion). And letting
> libarchive handle it directly might be more efficient.

How about making =CMD optional.  If it's missing, debuginfod would
assume "cat".  (I'd prefer not to have to change the code again for
some other distro that has a thin wrapper around a libarchive-readable
format, where something like rpm2cpio or dog would be needed.)


- FChE