Add `$schema` to `cgmanifest.json` (#9832)

Co-authored-by: Sean McManus <seanmcm@microsoft.com>

Extension/cgmanifest.json

@@ -1,24 +1,25 @@
 {
-    "Registrations": [
-        {
-            "Component": {
-                "Type": "git",
-                "Git": {
-                    "RepositoryUrl": "https://github.com/llvm/llvm-project",
-                    "CommitHash": "0d44201451f03ba907cdb268ddddfc3fa38a0ebd"
-                },
-                "DevelopmentDependency": true
-            }
+  "$schema": "https://json.schemastore.org/component-detection-manifest.json",
+  "Registrations": [
+    {
+      "Component": {
+        "Type": "git",
+        "Git": {
+          "RepositoryUrl": "https://github.com/llvm/llvm-project",
+          "CommitHash": "0d44201451f03ba907cdb268ddddfc3fa38a0ebd"
         },
-        {
-            "Component": {
-                "Type": "git",
-                "Git": {
-                    "RepositoryUrl": "https://github.com/lldb-tools/lldb-mi",
-                    "CommitHash": "2388bd74133bc21eac59b2e2bf97f2a30770a315"
-                }
-            }
+        "DevelopmentDependency": true
+      }
+    },
+    {
+      "Component": {
+        "Type": "git",
+        "Git": {
+          "RepositoryUrl": "https://github.com/lldb-tools/lldb-mi",
+          "CommitHash": "2388bd74133bc21eac59b2e2bf97f2a30770a315"
         }
-    ],
-    "Version": 1
-}
+      }
+    }
+  ],
+  "Version": 1
+}