feat: add an option to use github's auto merge (#302)

README.md

@@ -25,6 +25,18 @@ _Optional_ The merge method you would like to use (squash, merge, rebase). Defau
 
 _Optional_ An arbitrary message that you'd like to comment on the PR after it gets auto-merged. This is only useful when you're recieving too much of noise in email and would like to filter mails for PRs that got automatically merged.
 
+### `use-github-auto-merge`
+
+_Optional_ If `true`, the PR is marked as auto-merge and will be merged by GitHub when status checks are satisfied. Default to `false`.
+
+_NOTE_ This feature only works when all of the following conditions are met.
+
+- The repository enables auto-merge.
+- The pull request base must have a branch protection rule.
+- The pull request's status checks are not yet satisfied.
+
+Refer to [the official document](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/incorporating-changes-from-a-pull-request/automatically-merging-a-pull-request) about GitHub auto-merge.
+
 ### `target`
 
 _Optional_ A flag to only auto-merge updates based on Semantic Versioning. Defaults to `any`.

action.yml

@@ -21,6 +21,10 @@ inputs:
     description: "An arbitrary message that you'd like to comment on the PR after it gets auto-merged"
     required: false
     default: ''
+  use-github-auto-merge:
+    description: 'If true, the PR is only marked as auto-merge enabled'
+    required: false
+    default: false
   target:
     description: 'Auto-merge on major, minor, patch updates based on Semantic Versioning'
     required: false