build: migrate ng-dev config to .ng-dev directory (angular#37142)

Migrate to using .ng-dev directory for ng-dev configuration to allow better management of the configuration using multiple files. The intention is to prevent the config file from becoming unruly. PR Close angular#37142

Author: josephperrott

.ng-dev-config.ts renamed to .ng-dev/config.ts

@@ -1,4 +1,4 @@
-import {MergeConfig} from './dev-infra/pr/merge/config';
+import {MergeConfig} from '../dev-infra/pr/merge/config';
 
 // The configuration for `ng-dev commit-message` commands.
 const commitMessage = {

.pullapprove.yml

@@ -953,6 +953,7 @@ groups:
  '.circleci/**',
  '.devcontainer/**',
  '.github/**',
+ '.ng-dev/**',
  '.vscode/**',
  '.yarn/**',
  'dev-infra/**',