`gh stack submit` does not respect org-wide PR template

My organisation has an org-wide PR template, just as the one described here: https://github.com/orgs/community/discussions/183776. We used to have these templates in each repo, but they were all the same and repetitve, so we decided to define them in one place. We'd rather not go back to per-repo template.

Unfortunately, `gh stack submit` does not seem to respect them. User has two options with this command:
* By default it opens CLI dialog to enter PR's title and description. It doesn't use the org template
* `--auto` creates PR with some pre-populated footer and nothing else. Again no template is used.

The command supports repo-wide templates, thanks to https://github.com/github/gh-stack/pull/77, but this PR does not seem to take org-wide templates into account.

まず `gh stack submit` のエントリーポイントと、デフォルトダイアログおよび `--auto` の各パスを追跡します。その際、リポジトリ全体のテンプレートについては github/gh-stack pull request #77 をコンテキストとして使用します。組織全体の PR テンプレートを使って両方のモードを再現し、その後、結果の pull request にそのテンプレートが含まれ、既存のフッターが失われていないことを確認します。

索引モデルが issue の本文から書いたものです。