feat(vault): re-introduce vault plugin (#12753)

Co-authored-by: Carlo Sala <carlosalag@protonmail.com>

plugins/vault/README.md

@@ -0,0 +1,9 @@
+# Vault plugin
+
+This plugin adds completion for [Vault](https://www.vaultproject.io/), the secrets and sensitive data manager.
+
+To use it, add `vault` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... vault)
+```