feat(plugins): `octozen` shows an Octocat zen quote on startup (#5959)

Co-authored-by: NMarc Cornellà <hello@mcornella.com>

plugins/octozen/README.md

+# Octozen plugin
+
+Displays a zen quote from GitHub's Octocat on start up.
+
+To use it, add `octozen` to the plugins array in your zshrc file:
+
+```zsh
+plugins=(... octozen)
+```
+
+It defines a `display_octozen` function that fetches a GitHub Octocat zen quote.
+NOTE: Internet connection is required (will time out if not fetched in 2 seconds).

plugins/octozen/octozen.plugin.zsh

+# octozen plugin
+
+# Displays a zen quote from octocat
+function display_octozen() {
+  curl -m 2 -fsL "https://api.github.com/octocat"
+  add-zsh-hook -d precmd display_octozen
+}
+
+# Display the octocat on the first precmd, after the whole starting process has finished
+autoload -Uz add-zsh-hook
+add-zsh-hook precmd display_octozen