* Rework proto generation
The changes here are:
- Fix the default goal (using "default" target is not doing it).
- Bail out with a useful message if proto submodule is not checked
out.
- Replace the use of docker image with downloading the protoc binary
and building the gogofast plugin ourselves. This gives us a greater
control over the invocation of protoc.
- Use rsync to copy the generated code, instead of pax. Pax did not
work for me (it was complaining about the unknown -0 flag).
The control over the protoc invocation will be useful later, when we
will want to generate a code with data structures in one place and the
collector code elsewhere. The collector code may or may not depend on
gRPC, but data structures have no need for it. This split will happen
when we move the gRPC code out of the OTLP exporter module into a
submodule.
Getting rid of docker has the upside that the generated files do not
belong to root, so there is no hassle of changing the ownership of the
files, and it is not requires to use sudo for the `clean` target. And
not using docker is faster.
The downside of this work is that it depends on more tools: rsync,
unzip and wget. I can only hope that macOS users have those tools too,
and that those tools are invoked the same.
* Update protogen workflow
