Enable feature flag by default

This MR enables the store_first_mentioned_in_commit_on_issue_close
by default. It also makes a small change to store the `authored_date`
instead of the `committed_date`.

app/services/issues/close_service.rb

@@ -52,12 +52,12 @@ module Issues
     end
 
     def store_first_mentioned_in_commit_at(issue, merge_request)
-      return unless Feature.enabled?(:store_first_mentioned_in_commit_on_issue_close, issue.project)
+      return unless Feature.enabled?(:store_first_mentioned_in_commit_on_issue_close, issue.project, default_enabled: true)
 
       metrics = issue.metrics
       return if metrics.nil? || metrics.first_mentioned_in_commit_at
 
-      first_commit_timestamp = merge_request.commits(limit: 1).first&.date
+      first_commit_timestamp = merge_request.commits(limit: 1).first.try(:authored_date)
       return unless first_commit_timestamp
 
       metrics.update!(first_mentioned_in_commit_at: first_commit_timestamp)

changelogs/unreleased/202094-enable-ff-by-default.yml

+---
+title: Store first commit's authored_date for value stream calculation on merge
+merge_request: 26885
+author:
+type: changed

spec/services/issues/close_service_spec.rb

@@ -103,8 +103,8 @@ describe Issues::CloseService do
         subject { described_class.new(project, user).close_issue(issue, closed_via: closing_merge_request) }
 
         context 'when `metrics.first_mentioned_in_commit_at` is not set' do
-          it 'uses the first commit timestamp' do
-            expected = closing_merge_request.commits.first.date
+          it 'uses the first commit authored timestamp' do
+            expected = closing_merge_request.commits.first.authored_date
 
             subject
 

spec/services/merge_requests/merge_service_spec.rb

@@ -118,7 +118,7 @@ describe MergeRequests::MergeService do
 
       it 'closes GitLab issue tracker issues' do
         issue  = create :issue, project: project
-        commit = double('commit', safe_message: "Fixes #{issue.to_reference}", date: Time.now)
+        commit = instance_double('commit', safe_message: "Fixes #{issue.to_reference}", date: Time.now, authored_date: Time.now)
         allow(merge_request).to receive(:commits).and_return([commit])
         merge_request.cache_merge_request_closes_issues!