Add grpc-alts to grpc-all

This is to expose the code's javadoc and suppress the generated code's jacoco results. The main issue is suppressing the generated code's jacoco results, since the generated code is in the same package as the manually authored code.

The jacoco issue looks really ugly. We may need to rework our usage of the gradle plugin to compile the generated code into a separate destination directory, so then we can filter the entire directory instead of individual classes.

While it would be good to have a way to reliably filter generated code from jacoco results, it is probably easiest to move the generated code into a different package.