Generate release notes from PR labels (#265)

This change enables automatic release notes from labels. It also
enforces a changelog label for all PRs.

Categorizing changes will make it easier for users to understand what
changed in each release.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

## Chores
* Implemented automated changelog categorization and pull request label
enforcement to organize release notes into semantic sections (Added,
Changed, Fixed, Deprecated, Removed, Security, Dependencies) for
improved clarity in future releases.

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<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Signed-off-by: Philip Laine <philip.laine@gmail.com>

.github/workflows/changelog-labels.yaml

@@ -0,0 +1,20 @@
+name: changelog
+on:
+  pull_request:
+    types: [opened, labeled, unlabeled, synchronize]
+permissions:
+  pull-requests: read
+defaults:
+  run:
+    shell: bash
+jobs:
+  labels:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check changelog label
+        uses: mheap/github-action-required-labels@0ac283b4e65c1fb28ce6079dea5546ceca98ccbe #v5.5.2
+        with:
+          mode: exactly
+          count: 1
+          use_regex: true
+          labels: "changelog/.*"