ci: Group dependabot updates (#478)

Closes #462

Tries to avoid the flood of package updates by grouping them into
categories.
- Hugr packages get their own group
- Dev dependencies get grouped together as long as they are not breaking
changes.
- Patch releases and minor releases get their own groups
- Any major release gets its own PR

<img width="569" alt="image"
src="https://github.com/user-attachments/assets/b77387ba-0518-49b6-9d18-65f31825b4a6">

.github/dependabot.yml

@@ -12,13 +12,37 @@ updates:
     commit-message:
       # Use a conventional commit tag
       prefix: "chore(deps-rs)"
+    groups:
+      hugr:
+        patterns: ["hugr*"]
+      dev:
+        dependency-type: "development"
+        update-types: ["patch", "minor"]
+      patch:
+        update-types: ["patch"]
+      minor:
+        update-types: ["minor"]
+      # Major updates still generate individual PRs
+
   - package-ecosystem: "pip"
     directory: "/" # Location of package manifests
     schedule:
       interval: "weekly"
     commit-message:
       # Use a conventional commit tag
       prefix: "chore(deps-py)"
+    groups:
+      hugr:
+        patterns: ["hugr*"]
+      dev:
+        dependency-type: "development"
+        update-types: ["patch", "minor"]
+      patch:
+        update-types: ["patch"]
+      minor:
+        update-types: ["minor"]
+      # Major updates still generate individual PRs
+
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule: