ci: write down breaking change policy (#1294)

* Enforce conventional commit PR titles
* Add automatic labelling of PRs
* Write down breaking change policy.

Left for another PR:
* Validation of breaking change version bumps. (This is complicated due
to separate releases for Python and other package.)

.github/release.yml

@@ -0,0 +1,25 @@
+# TODO: create separate templates for Python and other releases.
+changelog:
+  exclude:
+    labels:
+      - ci
+      - chore
+  categories:
+    - title: Breaking Changes 🛠
+      labels:
+        - breaking-change
+    - title: New Features 🎉
+      labels:
+        - enhancement
+    - title: Bug Fixes 🐛
+      labels:
+        - bug
+    - title: Documentation 📚
+      labels:
+        - documentation
+    - title: Performance Improvements 🚀
+      labels:
+        - performance
+    - title: Other Changes
+      labels:
+        - "*"