Merge branch 'valexieva-scatter-flag' into 'master'

adding the scatterplot for productivity analytics flag

See merge request gitlab-org/gitlab!18748

doc/user/analytics/productivity_analytics.md

 # Productivity Analytics **(PREMIUM)**
 
-> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/12079) in [GitLab Premium](https://about.gitlab.com/pricing/) 12.3 (enabled by feature flags `productivity_analytics`).
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/12079) in [GitLab Premium](https://about.gitlab.com/pricing/) 12.3 (enabled by feature flags `productivity_analytics`, `productivity_analytics_scatterplot_enabled`).
 
 Track development velocity with Productivity Analytics.