chore: remove middleware to request version and entitlement warnings (#12750)

This cleans up `root.go` a bit, adds tests for middleware HTTP transport
functions, and removes two HTTP requests we always always performed previously
when executing *any* client command.

It should improve CLI performance (especially for users with higher latency).

enterprise/cmd/coder/main.go

@@ -8,5 +8,5 @@ import (
 
 func main() {
 	var rootCmd entcli.RootCmd
-	rootCmd.RunMain(rootCmd.EnterpriseSubcommands())
+	rootCmd.RunWithSubcommands(rootCmd.EnterpriseSubcommands())
 }