Consider adding new functionality to create proto archives

[ascopes]

A common pattern that I have seen is the use of zip archives containing protobuf sources
that are then added as a dependency by other projects.

Currently, if a Maven project wishes to create one of these ZIPs, it is a somewhat manual
process that involves setting up the Maven Archiver plugin in a specific way.

I think we could make that easier for users by potentially having a goal in this project that
concerns itself with generating these kinds of archives automatically.

One idea could be to introduce a new project packaging type that limits the Maven phases that get run so that only the required steps get called, e.g:

<project>
  ...
  <packaging>protobuf-zip</packaging>
  ...
</project>

This would then be able to register the ZIP as the project artifact for deployment to a Maven Central registry or similar.