add GitHub templates for PRs and releases

This commit adds:

1. a release template for GitHub releases.
2. a pull request template to help contributors and maintainers to understand and merge PRs faster, and label them correctly.

When using GitHub automated release notes, PRs will be split into sections based on the following labels:

- `breaking-change` or `config-change`
- `dependencies`
- `enhancement`
- `fix` or `bug`
- `plumbing`, `tests` or `deployment`
- all other PRs

Any labels not currently in use will be added once the PR for this commit is finalised and merged.

.github/release.yml

@@ -0,0 +1,26 @@
+changelog:
+  exclude:
+    labels:
+      - ignore-for-release
+  categories:
+    - title: ‼️ Breaking Changes & New Settings ⚙️
+      labels:
+        - breaking-change
+        - config-change
+    - title: Updated Dependencies 🧸
+      labels:
+        - dependencies
+    - title: New Features 🎉
+      labels:
+        - enhancement
+    - title: Bug Fixes 🐛
+      labels:
+        - fix
+        - bug
+    - title: Internals/Plumbing 👩‍🔧
+        - plumbing
+        - tests
+        - deployment
+    - title: Other Changes
+      labels:
+        - "*"