fix(dev-infra): allow for deep merging of pullapprove config aliases (#36915)

Set the yaml parser to support deep merges of yaml aliases,
to support having a default value for all rules to build upon.

PR Close #36915

dev-infra/pullapprove/parse-yaml.ts

@@ -31,5 +31,5 @@ export interface PullApproveConfig {
 }
 
 export function parsePullApproveYaml(rawYaml: string): PullApproveConfig {
-  return parseYaml(rawYaml) as PullApproveConfig;
+  return parseYaml(rawYaml, {merge: true}) as PullApproveConfig;
 }