Render the DAP Impact users by activity panel as a bar list

What does this MR do and why?

This MR switches the DAP Impact dashboard's "Users by activity" panel (Adoption tab) from a table to a barList, with valueLabels: value, color: blue, scale: max and maxRows: 20 under displayConfig, and adds showTrends: true to the visualization options so each row gets a previous-period trend pill. The as "Activity" / as "Users" aliases and the sort line are dropped, because the bar list sorts itself and has no column headers. The panel's grid height goes from 55 to 62 so up to 20 rows fit.

The change is a single file, ee/lib/gitlab/analytics/dashboards/system/dap_impact.yaml.

This MR depends on two other MRs:

• !254987 (merged), for the valueLabels, color and scale options and the trend pills.
• !254539 (merged) (merged), for the previous-period pairing helpers.

If this MR merges before the first, the panel still renders, but as a plain orange bar list with share-and-value labels and no trend pills, because unknown display options are ignored. The recommendation is to merge this after it.

References

Related issue: https://gitlab.com/gitlab-org/gitlab/-/work_items/628026 (DAP Impact V1: Users by activity visualization)

Depends on: !254987 (merged) and !254539 (merged)

The table this MR replaces was added in !254719 (merged)

Screenshots or screen recordings

"Before" is the table added in !254719 (merged). See that MR for its screenshots. "After" is the new bar list, rendered in dark mode with GDK data.

Before	After
See the screenshots in !254719 (merged)

How to set up and validate locally

1. Check out the branch of !254987 (merged), or wait until it is merged.
2. Check out this branch on top of it.
3. Run gdk restart rails-web.
4. Open http://127.0.0.1:3000/explore/analytics_dashboards/dap_impact?view=1 and choose a group in the scope picker.
5. Confirm the "Users by activity" panel shows blue bars with counts and trend pills.

MR acceptance checklist

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