Ensure GlSingleStat animates when data is changed

What does this MR do and why?

This MR ensures that the GlSingleStat component is only mounted once for VSA and MR analytics in order to allow the component to listen for changes and animate accordingly.

Screenshots or screen recordings

Screen_Recording_2021-10-21_at_10.41.04

How to set up and validate locally

• Browse to the MR Analytics and VSA features
  • http://127.0.0.1:3000/gitlab-org/gitlab-test/-/analytics/merge_request_analytics
  • http://127.0.0.1:3000/gitlab-org/gitlab-test/-/value_stream_analytics
• Play around with the filters to watch the animations

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 #335951 (closed)