build: replace ng-dev MergeConfig wiith PullRequestConfig

More info: angular/dev-infra@c3f5729

Author: alan-agius4

.ng-dev/config.ts

@@ -1,5 +1,5 @@
 export { commitMessage } from './commit-message';
 export { format } from './format';
 export { github } from './github';
-export { merge } from './merge';
+export { pullRequest } from './pull-request';
 export { release } from './release';

.ng-dev/merge.ts renamed to .ng-dev/pull-request.ts

@@ -1,10 +1,10 @@
-import { MergeConfig } from '@angular/dev-infra-private/ng-dev/pr/merge/config';
+import { PullRequestConfig } from '@angular/dev-infra-private/ng-dev/pr/config';
 
 /**
  * Configuration for the merge tool in `ng-dev`. This sets up the labels which
  * are respected by the merge script (e.g. the target labels).
  */
-export const merge: MergeConfig = {
+export const pullRequest: PullRequestConfig = {
   githubApiMerge: {
     default: 'rebase',
     labels: [{ pattern: 'squash commits', method: 'squash' }],