Use Dependabot to automatically update Go modules

It will submit updates to Kubernetes and OpenTelemetry separately from
other modules.

Author: cbandy

.github/dependabot.yml

@@ -5,16 +5,56 @@
 # documentation: https://docs.github.com/code-security/dependabot/dependabot-version-updates
 # schema documentation: https://docs.github.com/code-security/dependabot/working-with-dependabot/dependabot-options-reference
 # yaml-language-server: $schema=https://json.schemastore.org/dependabot-2.0.json
+#
+# Dependabot allows only one schedule per package-ecosystem, directory, and target-branch.
+# Configurations that lack a "target-branch" field also affect security updates.
+#
+# There is a hack to have *two* schedules: https://github.com/dependabot/dependabot-core/issues/1778#issuecomment-1988140219
 ---
 version: 2
 updates:
   - package-ecosystem: github-actions
     directories:
+      # "/" is a special case that includes ".github/workflows/*"
       - '/'
       - '.github/actions/*'
     schedule:
       interval: weekly
       day: tuesday
+    labels:
+      - dependencies
+    groups:
+      # Group security updates into one pull request
+      action-vulnerabilities:
+        applies-to: security-updates
+        patterns: ['*']
+
+      # Group version updates into one pull request
+      github-actions:
+        applies-to: version-updates
+        patterns: ['*']
+
+  - package-ecosystem: gomod
+    directory: '/'
+    schedule:
+      interval: weekly
+      day: wednesday
+    labels:
+      - dependencies
     groups:
-      all-github-actions:
+      # Group security updates into one pull request
+      go-vulnerabilities:
+        applies-to: security-updates
+        patterns: ['*']
+
+      # Group Kubernetes and OpenTelemetry version updates into separate pull requests
+      kubernetes:
+        patterns: ['k8s.io/*', 'sigs.k8s.io/*']
+      opentelemetry:
+        patterns: ['go.opentelemetry.io/*']
+      go-dependencies:
         patterns: ['*']
+        exclude-patterns:
+          - 'k8s.io/*'
+          - 'sigs.k8s.io/*'
+          - 'go.opentelemetry.io/*'