Merge branch 'productivity-analytics-docs' into 'master'

Add docs page for productivity_analytics

See merge request gitlab-org/gitlab-ce!31460

doc/user/analytics/productivity_analytics.md

+# Productivity Analytics **(PREMIUM)**
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab-ee/issues/12079) in [GitLab Premium](https://about.gitlab.com/pricing/) 12.2 (enabled by feature flags `analytics` and `productivity_analytics`).
+
+Track development velocity with Productivity Analytics.
+
+For many companies, the development cycle is a blackbox and getting an estimate of how
+long, on average, it takes to deliver features is an enormous endeavor.
+
+While [Cycle Analytics](../project/cycle_analytics.md) focuses on the entire
+SDLC process, Productivity Analytics provides a way for Engineering Management to
+drill down in a systematic way to uncover patterns and causes for success or failure at
+an individual, project or group level.
+
+Productivity can slow down for many reasons ranging from degrading code base to quickly
+growing teams. In order to investigate, department or team leaders can start by visualizing the time
+it takes for merge requests to be merged.
+
+## Supported features
+
+Productivity Analytics allows GitLab users to:
+
+- Visualize typical Merge Request lifetime and statistics. Use a histogram
+  that shows the distribution of the time elapsed between creating and merging
+  Merge Requests.
+- Drill down into the most time consuming Merge Requests, select a number of outliers,
+  and filter down all subsequent charts to investigate potential causes.
+- Filter by group, project, author, label, milestone, or a specific date range.
+  Filter down, for example, to the Merge Requests of a specific author in a group
+  or project during a milestone or specific date range.
+
+## Accessing metrics and visualizations
+
+To access the **Productivity Analytics** page, go to **Analytics > Productivity Analytics**.
+
+The following metrics and visualizations are available on a project or group level:
+
+- Histogram showing the number of Merge Request that took a specified number of days to
+  merge after creation. Select a specific column to filter down subsequent charts.
+- Histogram showing a breakdown of the time taken (in hours) to merge a Merge Request.
+  The following intervals are available:
+  - Time from first commit to first comment.
+  - Time from first comment until last commit.
+  - Time from last commit to merge.
+- Histogram showing the size or complexity of a Merge Request, using the following:
+  - Number of commits per Merge Request.
+  - Number of lines of code per commit.
+  - Number of files touched.
+- Table showing list of Merge Requests with their respective times and size metrics.
+  Can be sorted by the above metrics.
+  - Users can sort by any of the above metrics
+
+## Retrieving data
+
+Users can retrieve three months of data when they deploy Cycle Analytics for the first time.
+
+To retrieve data for a different time span, run the following in the GitLab directory:
+
+```sh
+MERGED_AT_AFTER = <your_date> rake gitlab:productivity_analytics:recalc
+```
+
+## Permissions
+
+The **Productivity Analytics** dashboard can be accessed only:
+
+- On GitLab instances and namespaces on
+  [Premium or Silver tier](https://about.gitlab.com/pricing/) and above.
+- By users with [Reporter access](../permissions.md) and above.