feat(ci): Add release-please automation with VERSION

* Add VERSION file that Zephyr will pick up
* Add release-please automation

.github/workflows/release-please.yml

@@ -0,0 +1,33 @@
+on:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: write
+  pull-requests: write
+
+name: release-please
+
+jobs:
+  release-please:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: googleapis/release-please-action@v4
+        with:
+          token: ${{ secrets.ZMK_RELEASE_PLEASE_TOKEN }}
+          release-type: simple
+      - name: tag major, minor, and patch versions
+        if: ${{ steps.release.outputs.release_created }}
+        run: |
+          git config user.name github-actions[bot]
+          git config user.email 41898282+github-actions[bot]@users.noreply.github.com
+          git remote add gh-token "https://x-access-token:${{ secrets.ZMK_RELEASE_PLEASE_TOKEN }}@github.com/${{ github.repository }}.git"
+          git tag -d v${{ steps.release.outputs.major }} || true
+          git tag -d v${{ steps.release.outputs.major }}.${{ steps.release.outputs.minor }} || true
+          git tag -a v${{ steps.release.outputs.major }} -m "Release v${{ steps.release.outputs.major }}"
+          git tag -a v${{ steps.release.outputs.major }}.${{ steps.release.outputs.minor }} -m "Release v${{ steps.release.outputs.major }}.${{ steps.release.outputs.minor }}"
+          git tag -a v${{ steps.release.outputs.major }}.${{ steps.release.outputs.minor }}.${{ steps.release.outputs.patch }} -m "Release v${{ steps.release.outputs.major }}.${{ steps.release.outputs.minor }}.${{ steps.release.outputs.patch }}"
+          git push --force gh-token v${{ steps.release.outputs.major }}
+          git push --force gh-token v${{ steps.release.outputs.major }}.${{ steps.release.outputs.minor }}
+          git push --force gh-token v${{ steps.release.outputs.major }}.${{ steps.release.outputs.minor }}.${{ steps.release.outputs.patch }}

.release-please-manifest.json

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+{
+  "extra-files": [
+    {
+      "type": "generic",
+      "path": "app/VERSION"
+    }
+  ]
+}

app/VERSION

@@ -0,0 +1,13 @@
+# x-release-please-start-major
+VERSION_MAJOR = 0
+# x-release-please-end
+
+# x-release-please-start-minor
+VERSION_MINOR = 0
+# x-release-please-end
+
+# x-release-please-start-patch
+PATCHLEVEL = 1
+# x-release-please-end
+
+VERSION_TWEAK = 0