Add rollout issue URLs for 2 Optimize feature flags

This adds missing rollout issue URLs to 2 feature flag definitions.

config/feature_flags/development/optimized_issuable_label_filter.yml

 ---
 name: optimized_issuable_label_filter
 introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/34503
-rollout_issue_url: 
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/259719
 milestone: '13.4'
 type: development
 group: group::optimize

config/feature_flags/development/track_unique_visits.yml

 ---
 name: track_unique_visits
 introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/33146
-rollout_issue_url: 
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/255994
 milestone: '13.2'
 type: development
 group: group::optimize