Now all regen PRs will include a block that mentions all of the
changes that happened in googleapis/googleapis that caused the
files to be generated. This information will eventually be fed
into our automated releases via release-please. There these changes
will be parsed out to add extra context to our release PRs and
changelogs. No longer will we have to have a vague message about
many auto-generated changes.

- Adds context to regen PRs.
- Refactored generators so every method does not need so many
  parameters.
- Updated goolge/protobuf to its new migrated repo
  protocolbuffers/protobuf.
- Added some extra logging to the build.
- Only run protoc on dirs that have changes.