Improve JanePHP recipes first-run experience (#2033)

* Improve JanePHP recipes first-run experience

Recipes pointed the generator configs to specification files they never
created, hid all generator output behind a NullOutput (so failures showed
up as raw PHP fatals and successes printed nothing) and always exited 0,
even when generation failed.

- document every config key and the spec file prerequisite in
  config/jane/*.php
- render generator output, format thrown errors and propagate exit codes
  in the recipe bin scripts
- reorder post-install steps: placing the specification file now comes
  before running the generator
- explain when/how to uncomment the generated normalizer service in
  config/packages/jane.yaml

Refs: https://github.com/janephp/janephp/issues/860

* Point recipes to the current documentation website

jane.readthedocs.io is outdated, jane.jolicode.com/latest/ is the
current documentation home.

* Re-trigger QA after adding the license header to the PR description

jane-php/open-api-common/7.0/config/jane/open_api.php

@@ -1,5 +1,19 @@
 <?php
 
+/*
+ * Jane OpenAPI generator configuration.
+ *
+ * - "openapi-file": path to your OpenAPI specification (JSON or YAML).
+ *   This file must exist before running bin/jane-open-api-generate:
+ *   either place your specification at config/jane/open-api.yaml,
+ *   or update this path to point to it.
+ * - "namespace": root namespace of the generated code. It must match the
+ *   PSR-4 mapping you add to your composer.json autoload section.
+ * - "directory": target directory for the generated files.
+ *
+ * See https://jane.jolicode.com/latest/ for all available options.
+ */
+
 return [
     'openapi-file' => __DIR__ . '/open-api.yaml',
     'namespace' => 'MyApp\Library\Generated',