Track total visits to value streams dashboard page

What does this MR do and why?

Count total number of visits to value streams dashboard page.

The metric should behave as follows:

1. time_frame: monthly, weekly
2. name: analytics_counts_visits.g_metrics_comparison_page
3. both SaaS and self-manage

Next step is to record unique views for the same page.

related to #384010 (closed)

How to set up and validate locally

Execute the following at a rails console:

  # Manually increment the count for the event, can be executed many time as wanted
  Gitlab::UsageDataCounters::ValueStreamsDashboardCounter.count(:views)

  # Build the payload
  payload = ServicePing::BuildPayload.new.execute

  # Check the recorded value
  payload['analytics_counts_visits']['g_metrics_comparison_page']

MR acceptance checklist

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