Having the modules stored in `./vendor` causes issues with `go mod`.
Follow waypoint's convention to store in `./thirdparty` and grab
the same Makefile modifications to alert when the submodules need
to be initialized. Update generators to use new path.
There are still some things left to address like how to handle
a target (or targets) and if that is something we should even
be doing. It may be best to just let the command deal with
target loading. There are also some considerations to make
around remote source.
