Give details about feature flags

Add info to FF yml files

config/feature_flags/development/similarity_search.yml

 ---
 name: similarity_search
-introduced_by_url: 
-rollout_issue_url: 
-group: 
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/37300/
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38675
+group: group::analytics
 type: development
 default_enabled: true

config/feature_flags/development/track_unique_visits.yml

 ---
 name: track_unique_visits
-introduced_by_url: 
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/33146
 rollout_issue_url: 
-group: 
+group: group::analytics
 type: development
 default_enabled: false

ee/config/feature_flags/development/analytics_similarity_search.yml

 ---
 name: analytics_similarity_search
-introduced_by_url: 
-rollout_issue_url: 
-group: 
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/37700
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38675
+group: group::analytics
 type: development
 default_enabled: true