Add initial files and templates for ps_emailalerts module

- Created LICENSE file for composer dependencies.
- Added autoload files: autoload_classmap.php, autoload_namespaces.php, autoload_psr4.php, autoload_real.php, and autoload_static.php.
- Initialized installed.json for composer.
- Added index.php and form templates for admin configuration.
- Implemented front-end templates for email alerts, including account management and product notifications.
- Included necessary headers and copyright notices in all new files.

modules/ps_emailalerts/CONTRIBUTORS.md

@@ -0,0 +1,11 @@
+GitHub contributors:
+--------------------------------
+- aleeks
+- antoin-m
+- AntoineMille
+- eternoendless
+- matks
+- maximebiloe
+- PierreRambaud
+- Progi1984
+- v4lux