Add devcontainer-lock.json with Renovate update support (#39046)

.devcontainer/devcontainer-lock.json

@@ -0,0 +1,9 @@
+{
+  "features": {
+    "ghcr.io/devcontainers/features/sshd:1": {
+      "version": "1.1.0",
+      "resolved": "ghcr.io/devcontainers/features/sshd@sha256:f5251b8e4325f68f7280973c6cd65daff414449c66f240621502d4e8e74eb7ee",
+      "integrity": "sha256:f5251b8e4325f68f7280973c6cd65daff414449c66f240621502d4e8e74eb7ee"
+    }
+  }
+}

.github/renovate.json5

@@ -15,6 +15,13 @@
   // to `null` after any other rule set it to something.
   dependencyDashboardHeader: 'This issue lists Renovate updates and detected dependencies. Read the [Dependency Dashboard](https://docs.renovatebot.com/key-concepts/dashboard/) docs to learn more. Before approving any upgrade: read the description and comments in the [`renovate.json5` file](https://github.com/mastodon/mastodon/blob/main/.github/renovate.json5).',
   postUpdateOptions: ['yarnDedupeHighest'],
+  devcontainer: {
+    managerFilePatterns: [
+      '/^\.devcontainer\/devcontainer\.json$/',
+      '/^\.devcontainer\.json$/',
+      '/^\.devcontainer\/devcontainer-lock\.json$/',
+    ],
+  },
   // The types are now included in recent versions,we ignore them here until we upgrade and remove the dependency
   ignoreDeps: ['@types/emoji-mart'],
   packageRules: [