feat(symfony6): Add plugin for native autocompletion from Symfony 6

This reverts commit 83014bd945.

plugins/symfony6/README.md

@@ -0,0 +1,9 @@
+# Symfony
+
+This plugin provides native completion for [Symfony](https://symfony.com/), but requires at least Symfony 6.2.
+
+To use it add `symfony6` to the plugins array in your zshrc file.
+
+```bash
+plugins=(... symfony6)
+```