No check for authentication before pushing packages

[ayys]

wasmer package push and friends do not properly check if the user
is authenticated before trying to push a package. This can lead to
confusing errors like this one:

ᳱ wasmer deploy --registry https://registry.wasmer.io/graphql --publish-package --non-interactive --token "wap_abcd"
Loading local package (manifest path: /home/ayush/git/docs.wasmer.io/.)
✔ Correctly built package locally
error: The backend did not provide a valid signed URL to upload the package

This error is very confusing, and implies an issue with the
registry. When in fact, the issue is with the user not being logged
in because the token is incorrect.