chore: satisfy Registrator AutoMerge guidelines automatically

Mirrors sotashimozono/Lattice2D.jl#23: makes release-drafter,
PRLabeler, PR template and AutoRegister wrap every drafted set of
release notes with a '## Changelog' header, so Registrator's
required 'breaking' / 'changelog' keyword is always present on the
'@JuliaRegistrator register' comment. Also adds the 'breaking'
label as a first-class citizen that forces a minor version bump.

Author: sotashimozono

.github/release-drafter.yml

@@ -1,32 +1,39 @@
-name-template: 'v$RESOLVED_VERSION'
-tag-template: 'v$RESOLVED_VERSION'
-version-resolver:
-  major:
-    labels: ['major']
-  minor:
-    labels: ['minor']
-  patch:
-    labels: ['patch']
-  default: patch
-categories:
-  - title: '🚀 Features'
-    labels:
-      - 'enhancement'
-      - 'feature'
-  - title: '🐛 Bug Fixes'
-    labels:
-      - 'bug'
-      - 'fix'
-  - title: '⚡ Performance'
-    labels:
-      - 'performance'
-  - title: '📖 Documentation'
-    labels:
-      - 'documentation'
-  - title: '🧰 Maintenance'
-    labels:
-      - 'chore'
-      - 'refactor'
-
-template: |
+name-template: 'v$RESOLVED_VERSION'
+tag-template: 'v$RESOLVED_VERSION'
+version-resolver:
+  major:
+    labels: ['major']
+  minor:
+    labels:
+      - 'minor'
+      - 'breaking'
+  patch:
+    labels: ['patch']
+  default: patch
+categories:
+  - title: '💥 Breaking changes'
+    labels:
+      - 'breaking'
+  - title: '🚀 Features'
+    labels:
+      - 'enhancement'
+      - 'feature'
+  - title: '🐛 Bug Fixes'
+    labels:
+      - 'bug'
+      - 'fix'
+  - title: '⚡ Performance'
+    labels:
+      - 'performance'
+  - title: '📖 Documentation'
+    labels:
+      - 'documentation'
+  - title: '🧰 Maintenance'
+    labels:
+      - 'chore'
+      - 'refactor'
+
+template: |
+  ## Changelog
+
   $CHANGES