chore: minor GitHub action changes (#17022)

* chore: run issue cleanup action more frequently

This changes the issue cleanup action to run 6 times per day (once every
four hours) insted of only once per day.

* chore: create action documentation

Documents each of the GitHub actions in the repo and their owners

.github/workflows/README.md

@@ -0,0 +1,47 @@
+# AWS CDK GitHub Actions
+
+These workflows and actions are configured in the AWS CDK GitHub repository.
+
+## Pull Request Triggered
+
+### Auto Approve
+[auto-approve.yml](auto-approve.yml): Approves merging PRs with the
+`pr/auto-approve` label.
+Owner: Core CDK team
+
+### PR Linter
+[pr-linter.yml](pr-linter.yml): Runs `tools/@aws-cdk-prlint` on each PR to
+check for correctness.
+Owner: Core CDK team
+
+### v2-main PR automation
+[v2-pull-request.yml](v2-pull-request.yml): Runs `pkglint` on merge forward PRs
+and commits the results.
+Owner: Core CDK team
+
+### Label Assigner
+[issue-label-assign.yml](issue-label-assign.yml): Github action for automatically adding labels and/or setting assignees when an Issue or PR is opened or edited based on user-defined Area
+Owner: CDK support team
+
+## Issue Triggered
+
+### Closed Issue Message
+[closed-issue-message.yml](closed-issue-message.yml): Adds a reminder message
+to issues that are closed.
+Owner: CDK support team
+
+### Label Assigner
+[issue-label-assign.yml](issue-label-assign.yml): Github action for automatically adding labels and/or setting assignees when an Issue or PR is opened or edited based on user-defined Area
+Owner: CDK support team
+
+## Scheduled Actions
+
+### Issue Lifecycle Handling
+[close-stale-issues.yml](close-stale-issues.yml): Handles labeling issues and
+PRs with `closing-soon`, `response-requested`, etc.
+Owner: CDK support team
+
+### Yarn Upgrader
+[yarn-upgrade.yml](yarn-upgrade.yml): Upgrades yarn dependencies and creates a
+patch file for downloading.
+Owner: Core CDK team

.github/workflows/close-stale-issues.yml

@@ -4,7 +4,7 @@ name: "Close Stale Issues"
 on:
   workflow_dispatch:
   schedule:
-  - cron: "0 6 * * *"
+  - cron: "0 */4 * * *"
 
 jobs:
   cleanup: