fix: support pack-based images that do not have a Procfile

If no Procfile is set, we'll leave the entrypoint alone, resulting in the default launcher for the web process (or whatever pack decided was default) executing.

Closes #5753

tests/unit/builder-pack.bats

@@ -75,6 +75,13 @@ teardown() {
   assert_output_contains 'Installing requirements with pip'
 }
 
+@test "(builder-pack) git:from-image without a Procfile" {
+  run /bin/bash -c "dokku git:from-image $TEST_APP dokku/smoke-test-gradle-app:1"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+}
+
 inject_requirements_txt() {
   local APP="$1"
   local APP_REPO_DIR="$2"