tweak(pre-commit): Automate manifest updates (#584)

Follow up from #583, start automating updating the manifest so we can
automate more merges.

---

### Changes are visible to end-users: no

### Test plan

N/A.

Author: arrdem

.pre-commit-config.yaml

@@ -44,3 +44,11 @@ repos:
         entry: /usr/bin/env bazel run //docs:update
         language: script
         files: \.bzl$
+
+  - repo: local
+    hooks:
+      - id: check-manifets
+        name: Update gazelle manifest
+        entry: /usr/bin/env bazel run //:gazelle_python_manifest.update
+        language: script
+        files: requirements.txt\$