Merge pull request #6211 from libgit2/ethomson/release_config

meta: add a release configuration file

.github/release.yml

+changelog:
+  categories:
+  - title: New features
+    labels:
+    - feature
+  - title: Bug fixes
+    labels:
+    - bug
+  - title: Code cleanups
+    labels:
+    - cleanup
+  - title: CI improvements
+    labels:
+    - build
+  - title: Documentation improvements
+    labels:
+    - documentation
+  - title: Other Changes
+    labels:
+      - '*'