feat(outputs): app-slug and installation-id (#105)

It is convenient to use `https://api.github.com/users/$app_slug[bot]` to
obtain the corresponding account ID later.
Then build `Signed-off-by: $app_slug[bot]
<$id+$app_slug[bot]@users.noreply.github.com>`.

Currently, there is no Linux environment to build test snapshot files

README.md

@@ -239,6 +239,14 @@ jobs:
 
 GitHub App installation access token.
 
+### `installation-id`
+
+GitHub App installation ID.
+
+### `app-slug`
+
+GitHub App slug.
+
 ## How it works
 
 The action creates an installation access token using [the `POST /app/installations/{installation_id}/access_tokens` endpoint](https://docs.github.com/rest/apps/apps?apiVersion=2022-11-28#create-an-installation-access-token-for-an-app). By default,