Add FF disable setting last_used_at on SSH access

This allows circumventing setting the `last_used_at` flag when
accessing repositories through git-ssh.

config/feature_flags/development/disable_ssh_key_used_tracking.yml

+---
+name: disable_ssh_key_used_tracking
+introduced_by_url:
+rollout_issue_url: https://gitlab.com/gitlab-com/gl-infra/scalability/-/issues/889
+milestone: '13.9'
+type: development
+group: group::source code
+default_enabled: false

lib/api/support/git_access_actor.rb

@@ -37,6 +37,8 @@ module API
       end
 
       def update_last_used_at!
+        return if Feature.enabled?(:disable_ssh_key_used_tracking)
+
         key&.update_last_used_at
       end
 

spec/lib/api/support/git_access_actor_spec.rb

@@ -152,6 +152,10 @@ RSpec.describe API::Support::GitAccessActor do
   end
 
   describe '#update_last_used_at!' do
+    before do
+      stub_feature_flags(disable_ssh_key_used_tracking: false)
+    end
+
     context 'when initialized with a User' do
       let(:user) { build(:user) }
 
@@ -170,6 +174,14 @@ RSpec.describe API::Support::GitAccessActor do
 
         subject.update_last_used_at!
       end
+
+      it 'does not update `last_used_at` when the functionality is disabled' do
+        stub_feature_flags(disable_ssh_key_used_tracking: true)
+
+        expect(key).not_to receive(:update_last_used_at)
+
+        subject.update_last_used_at!
+      end
     end
   end
 end