These changes address the following warning showing up on `go get`
operations:
go: module github.com/golang/protobuf is deprecated: Use the
"google.golang.org/protobuf" module instead.
All changes are made using the recommendations in the per-function
deprecation notices from the docs at
https://pkg.go.dev/github.com/golang/protobuf/ptypes
* Populate push configs when parsing the vagrantfile
* Allow untyped configs to be shipped over GRPC
* In our demo plugin, walk the vagrantfile and snag the config
Example Vagrantfile that works with the demo plugin:
```ruby
Vagrant.configure("2") do |config|
config.push.define "myplugin" do |push|
push.coolkey = "coolvalue"
push.alist = ["so", "many", "items"]
push.ahash = { "hashkey" => "hashvalue" }
end
end
```
