chore(renovate): group all Renovate updates together (#992)

This goes before the docs references, so they should take precedence for
regular docs-only file changes, and then we also make sure that docs are
included when there's a major update.

.github/renovate.json

@@ -2,6 +2,11 @@
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": ["github>renovatebot/.github", ":pinDependencies"],
   "packageRules": [
+    {
+      "description": "Always group updates to the Renovate Docker image",
+      "groupName": "renovate",
+      "matchPackageNames": ["ghcr.io/renovatebot/renovate"]
+    },
     {
       "description": "Update references in Markdown files weekly",
       "matchFileNames": ["**/*.md"],
@@ -14,6 +19,13 @@
       "semanticCommitScope": null,
       "additionalBranchPrefix": "docs-"
     },
+    {
+      "description": "Always group major updates to the Renovate Docker image (docs and code)",
+      "groupName": "renovate-major",
+      "matchUpdateTypes": ["major"],
+      "additionalBranchPrefix": "",
+      "matchPackageNames": ["ghcr.io/renovatebot/renovate"]
+    },
     {
       "description": "Use build semantic type for some deps",
       "matchPackageNames": ["@vercel/ncc", "typescript"],