Switch from mitchellh/cli to hashicorp/cli (#24239)

@mitchellh suggested we fork `cli` and switch to that.

Since we primarily use the interfaces in `cli`, and the new
fork has not changed those, this is (mostly) a drop-in replacement.

A small fix will be necessary for Vault Enterprise, I believe.

command/transit_import_key_version.go

@@ -6,7 +6,7 @@ package command
 import (
 	"strings"
 
-	"github.com/mitchellh/cli"
+	"github.com/hashicorp/cli"
 	"github.com/posener/complete"
 )