Migrate selected user_packages_total_unique_counts_monthly metric to Snowplow
Related Spike: https://gitlab.com/gitlab-org/product-intelligence/-/issues/470
Problem
In https://gitlab.com/gitlab-org/product-intelligence/-/issues/493 we selected experimental set of metrics. Now we need to send them using Snowplow.
Metric redis_hll_counters.user_packages.user_packages_total_unique_counts_monthly
is an HLL metric which is aggregated from 13 underlying metrics (https://gitlab.com/gitlab-org/gitlab/-/blob/master/config/metrics/counts_28d/20210216184937_user_packages_total_unique_counts_monthly.yml#L16) using this code within RedisHLLMetric https://gitlab.com/gitlab-org/gitlab/blob/master/lib/gitlab/usage/metrics/instrumentations/redis_hll_metric.rb#L29
Being added to usage_data https://gitlab.com/gitlab-org/gitlab/blob/master/lib/gitlab/usage_data.rb#L636
The actual event it tracked here https://gitlab.com/gitlab-org/gitlab/blob/master/app/helpers/packages_helper.rb#L46 (in API controllers)