Add workflow to close new feature PRs that haven't gone through a proposal process

Author: brophdawg11

.github/workflows/close-feature-pr.yml

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+# Close a singular pull request that implements a feature that has not
+# gone through the Proposal process
+# Triggered by adding the `feature-request` label to an issue
+
+name: 🚪 Close Feature Pull Request
+
+on:
+  pull_request:
+    types: [labeled]
+
+jobs:
+  close-feature-pr:
+    name: 🚪 Close Feature Pull Request
+    if: github.repository == 'remix-run/react-router' && github.event.label.name == 'feature-request'
+    runs-on: ubuntu-latest
+    steps:
+      - name: ⬇️ Checkout repo
+        uses: actions/checkout@v4
+
+      - name: 🚪 Close PR
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh pr comment ${{ github.event.pull_request.number }} -F ./scripts/close-feature-pr.md
+          gh pr edit ${{ github.event.pull_request.number }} --remove-label ${{ github.event.label.name }}
+          gh pr close ${{ github.event.pull_request.number }}

scripts/close-feature-pr.md

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+To align with our new [Open Governance](https://remix.run/blog/rr-governance) model, we are now asking that all new features go through the Proposal/RFC process and that we don't open PRs until a proposal has been been accepted and advanced to Stage 1.
+
+If this feature doesn't have a Proposal, please [open one](https://github.com/remix-run/react-router/discussions/new?category=proposals) so we can evaluate/discuss the proposed feature. You can link to this PR as an example of a potential implementation and we can re-open it if the proposal advances.
+
+If this PR already has a Proposal but it has not yet been accepted, let's continue the discussion in the Proposal until it gets accepted and then we can look to open a PR. Feel free to link to this PR or to a branch in a forked repo to show what a potential implementation might look like.
+
+If you have any questions, you can always reach out on [Discord](https://rmx.as/discord). Thanks again for providing feedback and helping us make React Router even better!