Add Stash toogle to display if there's some stash or not in `git_prompt_status`

lib/git.zsh

@@ -85,6 +85,9 @@ git_prompt_status() {
   elif $(echo "$INDEX" | grep '^AD ' &> /dev/null); then
     STATUS="$ZSH_THEME_GIT_PROMPT_DELETED$STATUS"
   fi
+  if $(git rev-parse --verify refs/stash >/dev/null 2>&1); then
+    STATUS="$ZSH_THEME_GIT_PROMPT_STASHED$STATUS"
+  fi
   if $(echo "$INDEX" | grep '^UU ' &> /dev/null); then
     STATUS="$ZSH_THEME_GIT_PROMPT_UNMERGED$STATUS"
   fi