Add direnv plugin (#8666)

plugins/direnv/README.md

+# direnv plugin
+
+This plugin creates the [Direnv](https://direnv.net/) hook.
+
+To use it, add `direnv` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... direnv)
+```
+
+## Requirements
+
+In order to make this work, you will need to have the direnv installed.
+
+More info on the usage and install: https://github.com/direnv/direnv

plugins/direnv/direnv.plugin.zsh

+_direnv_hook() {
+  trap -- '' SIGINT;
+  eval "$("/usr/local/bin/direnv" export zsh)";
+  trap - SIGINT;
+}
+typeset -ag precmd_functions;
+if [[ -z ${precmd_functions[(r)_direnv_hook]} ]]; then
+  precmd_functions=( _direnv_hook ${precmd_functions[@]} )
+fi
+typeset -ag chpwd_functions;
+if [[ -z ${chpwd_functions[(r)_direnv_hook]} ]]; then
+  chpwd_functions=( _direnv_hook ${chpwd_functions[@]} )
+fi