Attempt to generate protos nightly (#1042)

Make everyone's life easier by automating the `gen_protos` call to nightly. If it gets too annoying, we can reduce the frequency.

This idea came from a discussion with @insipx.

Here is a partial success https://github.com/xmtp/libxmtp/actions/runs/10775820735/job/29881125202

We can't confirm that this works until it lands in `main`. It has `dispatch` so that it can be tested, from there on, its nightly.

.github/workflows/nightly-protos.yml

@@ -0,0 +1,35 @@
+name: Nightly Automation
+on:
+  schedule:
+    - cron:  '0 10 * * 1'
+  workflow_dispatch:
+jobs:
+  nightly-protos:
+    permissions:
+      contents: write
+      pull-requests: write
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: bufbuild/buf-setup-action@v1.40.1
+      - name: Update rust toolchains
+        run: rustup update
+      - name: Cache
+        uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: |
+           .
+      - name: Generate Protos
+        run: dev/gen_protos.sh
+      - name: Create Pull Request
+        uses: peter-evans/create-pull-request@v7
+        with:
+          commit-message: Nightly Protos
+          title: Update Protos
+          body: |
+            - Nightly Proto Update
+
+            Auto-generated by [create-pull-request][1]
+
+            [1]: https://github.com/peter-evans/create-pull-request
+          branch: nightly-proto