build: migrate to new dependabot config (#20727)

Migrates to the new dependabot config rolled out since dependabot was
moved into Github.

Author: josephperrott

.dependabot/config.yml

@@ -342,7 +342,6 @@
 /.github/**                                        @angular/dev-infra-components
 /.github/CODEOWNERS                                @angular/dev-infra-components @jelbourn
 /.github/ISSUE_TEMPLATE/**                         @andrewseguin @jelbourn
-/.dependabot/**                                    @angular/dev-infra-components
 /.vscode/**                                        @angular/dev-infra-components @mmalerba
 /.ng-dev/**                                        @angular/dev-infra-components
 /goldens/size-test.yml                             @jelbourn @mmalerba @crisbeto

.github/CODEOWNERS

@@ -0,0 +1,12 @@
+version: 2
+
+updates:
+  - package-ecosystem: "npm"
+    directory: "/"
+    commit-message:
+      prefix: "build"
+    labels:
+      - "area: build"
+      - "merge ready"
+      - "merge safe"
+      - "target: patch"