Change proto package author from `albert.cui@pachyderm.io` to `python-pachyderm@pachyderm.io`

[msteffen]

When @albscui created the initial python-pachyderm proto package, he set himself as the package author for expediency. However, to make sure that future contributors to the package have access to bugs/questions/whatever, we should instead attach the package to a flexible email alias

[albscui]

For context: pachyderm/pachyderm#6182