Default enable use_upsert_query_for_mr_metrics FF

This change enables the use_upsert_query_for_mr_metrics feature flag by
default.

Changelog: changed

app/models/merge_request.rb

@@ -1869,7 +1869,7 @@ class MergeRequest < ApplicationRecord
 
   override :ensure_metrics
   def ensure_metrics
-    if Feature.enabled?(:use_upsert_query_for_mr_metrics)
+    if Feature.enabled?(:use_upsert_query_for_mr_metrics, default_enabled: :yaml)
       MergeRequest::Metrics.record!(self)
     else
       # Backward compatibility: some merge request metrics records will not have target_project_id filled in.

config/feature_flags/development/use_upsert_query_for_mr_metrics.yml

@@ -5,4 +5,4 @@ rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/339677
 milestone: '14.3'
 type: development
 group: group::optimize
-default_enabled: false
+default_enabled: true