This allows us to remove the manual replace directives
github.com/dgrijalva/jwt-go and google.golang.org/grpc, so that we can
remove the CVE warnings and update the grpc packages.
While the etcdv3 backend is also marked as deprecated, the changes here
are done in a manner to keep that backend working for the time being.
This is part of a general effort to move all of Terraform's non-library
package surface under internal in order to reinforce that these are for
internal use within Terraform only.
If you were previously importing packages under this prefix into an
external codebase, you could pin to an earlier release tag as an interim
solution until you've make a plan to achieve the same functionality some
other way.
