Migrate symbol package metrics to internal events

What does this MR do and why?

Related to #424893 (closed)

This is the last stage of migrating package events, started with pull events migration.

MR acceptance checklist

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Before	After

How to set up and validate locally

1. On master branch, in the ruby console, trigger all the migrated events: %w[i_package_nuget_pull_symbol_package i_package_nuget_push_symbol_package i_package_pull_symbol_package i_package_pull_symbol_package_by_deploy_token i_package_pull_symbol_package_by_guest i_package_pull_symbol_package_by_user i_package_push_symbol_package i_package_push_symbol_package_by_deploy_token i_package_push_symbol_package_by_guest i_package_push_symbol_package_by_user].each {|ev| ::Gitlab::UsageDataCounters::PackageEventCounter.count(ev)}
2. Calculate the metrics values: metrics = %w[counts.package_events_i_package_nuget_pull_symbol_package counts.package_events_i_package_nuget_push_symbol_package counts.package_events_i_package_pull_symbol_package counts.package_events_i_package_pull_symbol_package_by_deploy_token counts.package_events_i_package_pull_symbol_package_by_guest counts.package_events_i_package_pull_symbol_package_by_user counts.package_events_i_package_push_symbol_package counts.package_events_i_package_push_symbol_package_by_deploy_token counts.package_events_i_package_push_symbol_package_by_guest counts.package_events_i_package_push_symbol_package_by_user]; sp = Gitlab::Usage::ServicePing::InstrumentedPayload.new(metrics, :with_value).build
3. Check out this MR's branch and reload! the console
4. Make sure that all the metrics have the same values: sp2 = Gitlab::Usage::ServicePing::InstrumentedPayload.new(metrics, :with_value).build and then verify that sp == sp2 returns true
5. Trigger all of the events again: %w[push_symbol_package_to_registry pull_symbol_package_from_registry].each {|e| %w[deploy_token guest user].each {|p| Gitlab::InternalEvents.track_event(e, additional_properties: { label: 'nuget', property: p })}}
6. Generate new metric values sp3 = Gitlab::Usage::ServicePing::InstrumentedPayload.new(metrics, :with_value).build
7. Make sure that all the metrics values have increased: sp3.values.first.map {|k, v| v > sp2[:counts][k]}.uniq should return [true]