CLI import target validation for incorrect for_each keys (#3106)

Signed-off-by: Ilia Gogotchuri <ilia.gogotchuri0@gmail.com>

internal/command/testdata/import-keyed-module/child/main.tf

@@ -0,0 +1,6 @@
+variable "id" {
+  type = string
+}
+
+resource "test_instance" "this" {
+}

internal/command/testdata/import-keyed-module/main.tf

@@ -0,0 +1,10 @@
+locals {
+  items = toset(["a", "b"])
+}
+
+module "child" {
+  source   = "./child"
+  for_each = local.items
+
+  id = each.key
+}