`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.

先追蹤 `gh stack submit` 進入點及其預設對話框和 `--auto` 路徑，並以 github/gh-stack pull request #77 作為整個 repository 模板的背景。使用組織範圍的 PR 模板重現這兩種模式，然後驗證產生的 pull request 包含該模板，且不會遺失現有的 footer。

由索引模型根據 Issue 內容生成。