git: add `grename` to rename a local branch and in the origin remote (#8622)

Co-authored-by: Marc Cornellà <marc.cornella@live.com>

plugins/git/git.plugin.zsh

@@ -256,3 +256,17 @@ alias glum='git pull upstream master'
 
 alias gwch='git whatchanged -p --abbrev-commit --pretty=medium'
 alias gwip='git add -A; git rm $(git ls-files --deleted) 2> /dev/null; git commit --no-verify --no-gpg-sign -m "--wip-- [skip ci]"'
+
+function grename() {
+  if [[ -z "$1" || -z "$2" ]]; then
+    echo "Usage: $0 old_branch new_branch"
+    return 1
+  fi
+
+  # Rename branch locally
+  git branch -m "$1" "$2"
+  # Rename branch in origin remote
+  if git push origin :"$1"; then
+    git push --set-upstream origin "$2"
+  fi
+}