Add Submodule Release Updater GitHub Action and Workflow [Rebase & FF]

.github/actions/submodule-release-updater/ReadMe.md

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+# Project Mu Submodule Release Updater GitHub Action
+
+This GitHub Action checks if new releases are available for submodules and creates pull requests to update
+them. A single pull request is opened per submodule. At this time, the action should only be used within
+Project Mu repositories.
+
+## How to Use
+
+1. Create a GitHub workflow in a repository
+2. Add this GitHub Action as a step to the workflow
+3. Configure the workflow to trigger as desired
+   - It is recommended to trigger the workflow on a schedule (e.g. daily) to check for new releases.
+
+### Example Workflow
+
+```yaml
+name: Update Submodules to Latest Release
+
+on:
+  schedule:
+    - cron: '0 0 * * MON'  # https://crontab.guru/every-monday
+
+jobs:
+  repo_submodule_update:
+    name: Check for Submodule Releases
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Update Submodules to Latest Release
+        uses: microsoft/mu_devops/.github/actions/[email protected]
+        with:
+          GH_PAT: ${{ secrets.SUBMODULE_UPDATER_TOKEN }}
+          GH_USER: "Add GitHub account username here"
+          GIT_EMAIL: "Add email address here"
+          GIT_NAME: "Add git author name here"
+
+```
+
+## Action Inputs
+
+- `GH_PAT` - **Required** - GitHub Personal Access Token (PAT) with `repo` scope
+- `GH_USER` - **Required** - GitHub username
+- `GIT_EMAIL` - **Required** - Email address to use for git commits
+- `GIT_NAME` - **Required** - Name to use for git commits
+
+## Action Outputs
+
+- `submodule-update-count` - Number of submodules updated. `0` if no submodules were updated.
+
+## Limitations
+
+- This action is only intended to work within Project Mu repositories.
+- This action only supports repositories hosted on GitHub.
+- This action only updates submodules that are hosted on GitHub.
+- This action is only intended to work with submodules that use [semantic versioning](https://semver.org/).
+- Submodules should already be set to a specific release before enabling this action.
+  - This allows the action to compare new versions to the current version.
+- This action does not automatically close stale PRs when a new release is available.