add a command package test that shows that we can still have provider…

…s with dynamic configuration + required + interactive input merging

This test failed when buildProviderConfig still used configs.MergeBodies instead of hcl.MergeBodies

internal/command/testdata/plan-provider-input/main.tf

@@ -0,0 +1,20 @@
+variable "users" {
+    default = {
+        one = "onepw"
+        two = "twopw"
+    }
+}
+
+provider "test" {
+    url = "example.com"
+
+    dynamic "auth" {
+        for_each = var.users
+        content {
+            user     = auth.key
+            password = auth.value
+        }
+    }
+}
+
+resource "test_instance" "test" {}