feat: enable incus support in actionsdind container (#10)

- add incus-images backend
- set incus-images as default backend

Reviewed-on: https://git.query.consul/unkin/packer-images/pulls/10

builds/docker.pkr.hcl

@@ -21,6 +21,18 @@ build {
     destination = "/"
   }
 
+  # manage deploying incus client certficates
+  # this isnt super-secure, as the key ends up baked into the docker image
+  provisioner "shell" {
+    inline = [
+      "if [ ${var.include_incus_client_certs} = true ]; then",
+      "  mkdir -p /root/.config/incus",
+      "  echo '${replace(local.incus_crt, "'", "'\\''")}' > /root/.config/incus/client.crt",
+      "  echo '${replace(local.incus_key, "'", "'\\''")}' > /root/.config/incus/client.key",
+      "fi"
+    ]
+  }
+
   # post-file-copy scripts
   provisioner "shell" {
     inline = var.scripts_post_file_copy