git: add alias to `git stash --all` (#5511)

Stash tracked, ignored and untracked files. Leaves the working directory absolutely clean.

plugins/git/git.plugin.zsh

@@ -239,6 +239,7 @@ alias gstd='git stash drop'
 alias gstl='git stash list'
 alias gstp='git stash pop'
 alias gsts='git stash show --text'
+alias gstall='git stash --all'
 alias gsu='git submodule update'
 
 alias gts='git tag -s'