Copy preview workflow to main for manual workflow_dispatch usage

Author: brophdawg11

.github/workflows/preview.yml

@@ -0,0 +1,78 @@
+# Create "installable" preview branches
+#
+# Commits to `dev` push builds to a `preview/dev` branch:
+#   pnpm install "remix-run/react-router#preview/dev&path:packages/react-router"
+#
+# Can also be dispatched manually with base/installable branches to provide
+# `experimental` branches from PRs or otherwise.
+
+name: Preview Build
+
+on:
+  push:
+    branches:
+      - dev
+  workflow_dispatch:
+    inputs:
+      baseBranch:
+        description: Base Branch
+        required: true
+      installableBranch:
+        description: Installable Branch
+        required: true
+
+concurrency:
+  # Include `event_name` here because when a pull_request is merged (closed), the
+  # `github.ref` goes back to `ref/heads/dev` which will conflict with the run on
+  # `dev` from the merged PR
+  group: ${{ github.workflow }}-${{ github.event_name }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  preview:
+    if: github.repository == 'remix-run/react-router'
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout (push)
+        if: github.event_name == 'push'
+        uses: actions/checkout@v4
+
+      - name: Checkout (workflow_dispatch)
+        if: github.event_name == 'workflow_dispatch'
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ inputs.baseBranch }}
+
+      - name: Install pnpm
+        uses: pnpm/action-setup@v4
+
+      - name: Install Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version-file: "package.json"
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Setup git
+        run: |
+          git config --local user.email "hello@remix.run"
+          git config --local user.name "Remix Run Bot"
+
+      # Build and force push over the preview/dev branch
+      - name: Build/push branch (push)
+        if: github.event_name == 'push'
+        run: |
+          pnpm run setup-installable-branch preview/dev
+          git push --force --set-upstream origin preview/dev
+          echo "💿 pushed installable branch: https://github.com/$GITHUB_REPOSITORY/commit/$(git rev-parse HEAD)"
+
+      # Build and normal push for experimental releases to avoid unintended force
+      # pushes over remote branches in case of a branch name collision
+      - name: Build/push branch (workflow_dispatch)
+        if: github.event_name == 'workflow_dispatch'
+        run: |
+          pnpm run setup-installable-branch ${{ inputs.installableBranch }}
+          git push --set-upstream origin ${{ inputs.installableBranch }}
+          echo "💿 pushed installable branch: https://github.com/$GITHUB_REPOSITORY/commit/$(git rev-parse HEAD)"