Migrate value_streams_dashboard to internal events

What does this MR do and why?

Related to gitlab-org/analytics-section/analytics-instrumentation/internal#702 (moved)

This migrates the analytics_counts_visits.g_metrics_comparison_page total count metric to Internal Events, while keeping the original Redis key. Instead of migrating the key to the new format in TotalCountMetric, the new key is aliased in a YAML file and points to the old one, so that the count continues in the old key and we can keep the past count.

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Before	After

How to set up and validate locally

1. Checkout master and fire the event a few times (visit the value_streams_dashboard view).
2. Run in console and note the value:

definition = Gitlab::Usage::MetricDefinition.definitions['analytics_counts_visits.g_metrics_comparison_page']
Gitlab::Usage::Metric.new(definition).with_value

1. Enable the feature: Feature.enable(:group_analytics_dashboard_dynamic_vsd)
2. Checkout MR branch, reload! the console and run the previous point's code in the console again. The value should be identical.
3. Fire the event a few more times and make sure that the value got incremented.