support for .tar.gz archives as input of govpp apigen

[sknat]

It would be nice to be able to pass an archive as an input to the apigen cli, i.e. :

//go:generate go run go.fd.io/govpp/cmd/binapi-generator --gen rpc -o ./bindings --input ./somefile.tar.gz

Where ./somefile.tar.gz contains

core/
  ip_types.api.json
  ip.api.json
  ...
plugins/
  abf.api.json
  acl.api.json
  ...

In some cases, the api specification is exchanged as a compressed bundle,
having this feature would spare the caller the hassle to (decompress ; pass the temporary directory as input ; cleanup)