github automation improvements (#367)

Enable some ✨ fancy ✨ GitHub features to help maintenance and release
activities:

1. dependabot: group HashiCorp Go library updates together when possible
1. setup an initial `.github/release.yml` to help get CHANGELOG updates
closer to the right format automatically

.github/dependabot.yaml

@@ -5,7 +5,15 @@ updates:
     directory: "/"
     schedule:
       interval: "daily"
+    labels:
+      - dependencies
+    groups:
+      hashicorp:
+        patterns:
+          - "github.com/hashicorp/*"
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
       interval: "daily"
+    labels:
+      - dependencies

.github/release.yml

@@ -0,0 +1,22 @@
+changelog:
+    exclude:
+        labels:
+            - no-changelog
+    categories:
+        - title: NOTES
+          labels:
+              - breaking-change
+        - title: ENHANCEMENTS
+          labels:
+              - improvement
+              - feature
+        - title: BUGFIXES
+          labels:
+              - bug
+        - title: HOUSEKEEPING
+          labels:
+              - refactor
+              - dependencies
+        - title: Other Changes
+          labels:
+              - "*"