ci: adopt Renovate for dependency updates

.github/dependabot.yml

@@ -1,17 +0,0 @@
----
-version: 2
-updates:
-  - package-ecosystem: github-actions
-    directory: /
-    schedule:
-      interval: monthly
-    # One PR per repo instead of one per action; the workflow is generated from
-    # Axis_Cam_Template/ci/build.yml.tmpl, so apply bumps there and re-sync.
-    groups:
-      github-actions:
-        patterns:
-          - "*"
-    commit-message:
-      prefix: ci
-    labels:
-      - dependencies

renovate.json

@@ -0,0 +1,20 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": ["config:recommended"],
+  "dependencyDashboard": true,
+  "ignorePaths": [
+    ".github/workflows/build.yml"
+  ],
+  "prConcurrentLimit": 3,
+  "prHourlyLimit": 0,
+  "schedule": ["before 5am on Monday"],
+  "packageRules": [
+    {
+      "description": "Keep routine Go transitive dependency maintenance together.",
+      "matchManagers": ["gomod"],
+      "matchDepTypes": ["indirect"],
+      "groupName": "Go indirect dependencies",
+      "groupSlug": "go-indirect-dependencies"
+    }
+  ]
+}