Round deployment frequency avg. to nearest 10th

What does this MR do and why?

In the data labels on the sparkline chart for Deployment Frequency in a Value Stream Dashboard, round deployments per day numbers to the nearest tenth. This avoids unnecessarily precise data displays. This was raised in #416429 (closed).

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. On the master branch of gitlab:
2. If you don't already have a VSA group imported in your gdk, first run FILTER=cycle_analytics SEED_VSA=1 bundle exec rake db:seed_fu
3. Navigate to http://gdk.test:3000/groups/GROUP_NAME/-/analytics/dashboards/value_streams_dashboard, where GROUP_NAME is the name of the group created by the rake task above.
   • you should see that the "Deployment Frequency" sparkline graph for the Past 6 Months has very precise data points (for example, 24.193548387096776)
4. Check out this branch and reload VSD page in the browser
   • you should see that the data labels for the Deployment Frequency sparkline are all rounded to the nearest tenth (for example, 24.2)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #416429 (closed)