Add package metadata to `go_repository`s (#1852)

**What type of PR is this?**

Feature

**What package or component does this PR mostly affect?**

go_repository

**What does this PR do? Why is it needed?**

All targets in a `go_repository` with generated build files are tagged
with a `package_info` automatically created by the repo rule.

This PR does not add any license information yet.

**Which issues(s) does this PR fix?**

Work towards #1314 

**Other notes for review**