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

tests/main-repo-skew.js

@@ -9,6 +9,7 @@ await test((mockPool) => {
   const owner = process.env.INPUT_OWNER
   const repo = process.env.INPUT_REPOSITORIES
   const mockInstallationId = "123456";
+  const mockAppSlug = "github-actions";
 
   install({ now: 0, toFake: ["Date"] });
 
@@ -44,7 +45,8 @@ await test((mockPool) => {
       return {
         statusCode: 200,
         data: {
-          id: mockInstallationId
+          id: mockInstallationId,
+          "app_slug": mockAppSlug
         },
         responseOptions: {
           headers: {