Add Symfony Deprecation Contracts package

- Created CHANGELOG.md to maintain version history.
- Added README.md with usage instructions for the trigger_deprecation() function.
- Initialized composer.json for the Symfony Deprecation Contracts library, specifying dependencies and autoloading.

modules/pshowsso/deps/psr/http-factory/README.md

@@ -0,0 +1,12 @@
+HTTP Factories
+==============
+
+This repository holds all interfaces related to [PSR-17 (HTTP Factories)][psr-url].
+
+Note that this is not a HTTP Factory implementation of its own. It is merely interfaces that describe the components of a HTTP Factory.
+
+The installable [package][package-url] and [implementations][implementation-url] are listed on Packagist.
+
+[psr-url]: https://www.php-fig.org/psr/psr-17/
+[package-url]: https://packagist.org/packages/psr/http-factory
+[implementation-url]: https://packagist.org/providers/psr/http-factory-implementation