ci: create workflow which populates github actions cache

Author: galargh

.github/workflows/cache.yml

@@ -0,0 +1,44 @@
+name: Cache
+
+on:
+  push:
+    branches:
+      - main
+      - pre-release-testing-branch
+      - changeset-release/main
+      - v-next
+    paths:
+      - ".github/workflows/cache.yml"
+      - "**/pnpm-lock.yaml"
+  pull_request:
+    paths:
+      - ".github/workflows/cache.yml"
+      - "**/pnpm-lock.yaml"
+  workflow_dispatch:
+
+concurrency:
+  group: ${{github.workflow}}-${{github.ref}}
+  cancel-in-progress: true
+
+jobs:
+  cache:
+    name: Cache
+    runs-on: ${{ matrix.runner }}
+    strategy:
+      fail-fast: false
+      matrix:
+        runner: ["ubuntu-latest", "macos-latest", "windows-latest"]
+    steps:
+      - uses: actions/checkout@v4
+      - id: env
+        uses: ./.github/actions/setup-env
+        with:
+          cache-save: true
+      - name: Install
+        if: steps.env.outputs.cache-hit != 'true'
+        run: |
+          for lockfile in $(find "$(pwd)" -name pnpm-lock.yaml); do
+            pushd "$(dirname "$lockfile")"
+              pnpm install --frozen-lockfile --prefer-offline
+            popd
+          done