Add an autofix workflow (#44922)

One of the major annoyances with writing code with claude is that its
poorly indented; instead of requiring manual intervention, let's just
fix that in CI.

Similar to https://autofix.ci, but as we already have a github app,
we can do it without relying on a 3rd party.

This PR doesn't trigger the workflow (we need a separate change in Zippy
to do
that) but will let me test it manually.

Release Notes:

- N/A

.github/workflows/autofix_pr.yml

@@ -0,0 +1,53 @@
+# Generated from xtask::workflows::autofix_pr
+# Rebuild with `cargo xtask workflows`.
+name: autofix_pr
+run-name: 'autofix PR #${{ inputs.pr_number }}'
+on:
+  workflow_dispatch:
+    inputs:
+      pr_number:
+        description: pr_number
+        required: true
+        type: string
+jobs:
+  run_autofix:
+    runs-on: namespace-profile-2x4-ubuntu-2404
+    steps:
+    - id: get-app-token
+      name: autofix_pr::run_autofix::authenticate_as_zippy
+      uses: actions/create-github-app-token@bef1eaf1c0ac2b148ee2a0a74c65fbe6db0631f1
+      with:
+        app-id: ${{ secrets.ZED_ZIPPY_APP_ID }}
+        private-key: ${{ secrets.ZED_ZIPPY_APP_PRIVATE_KEY }}
+    - name: steps::checkout_repo_with_token
+      uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
+      with:
+        clean: false
+        token: ${{ steps.get-app-token.outputs.token }}
+    - name: autofix_pr::run_autofix::checkout_pr
+      run: gh pr checkout ${{ inputs.pr_number }}
+      shell: bash -euxo pipefail {0}
+      env:
+        GITHUB_TOKEN: ${{ steps.get-app-token.outputs.token }}
+    - name: autofix_pr::run_autofix::run_cargo_fmt
+      run: cargo fmt --all
+      shell: bash -euxo pipefail {0}
+    - name: autofix_pr::run_autofix::run_clippy_fix
+      run: cargo clippy --workspace --release --all-targets --all-features --fix --allow-dirty --allow-staged
+      shell: bash -euxo pipefail {0}
+    - name: autofix_pr::run_autofix::commit_and_push
+      run: |
+        if git diff --quiet; then
+            echo "No changes to commit"
+        else
+            git add -A
+            git commit -m "Apply cargo fmt and clippy --fix"
+            git push
+        fi
+      shell: bash -euxo pipefail {0}
+      env:
+        GIT_COMMITTER_NAME: Zed Zippy
+        GIT_COMMITTER_EMAIL: hi@zed.dev
+        GIT_AUTHOR_NAME: Zed Zippy
+        GIT_AUTHOR_EMAIL: hi@zed.dev
+        GITHUB_TOKEN: ${{ steps.get-app-token.outputs.token }}