Migrate epic events to internal events: vol.1

What does this MR do and why?

Related to #421593 (closed)

Migrate some of the redis_hll_counters.epics_usage.epics_usage_total_unique_counts_monthly event's sub-events to Internal Events API.

Script used to update the files:

class DebugGenerator < Gitlab::Analytics::InternalEventsGenerator
  source_root File.expand_path('generator_templates/gitlab_internal_events', __dir__)

  def create_metric_file
    validate!

    template "event_definition.yml",
      event_file_path(event),
      options.fetch(:event_desc)
  end
end

is_ee = true
mr_number = 131794
unique_by = "user.id"
section = "dev"
stage = "plan"
group = "product_planning"
events_with_desc = [
['g_project_management_epic_created', 'An epic has been created'],
['g_project_management_users_updating_epic_titles', "An epic's title has been updated"],
['g_project_management_users_updating_epic_descriptions', "An epic's description has been updated"]
]

events_with_desc.each do |event_name, event_desc|
  tiers = %w[premium ultimate]
  tiers = %w[free premium ultimate] if !is_ee
  DebugGenerator.new([], {
    event: event_name,
    event_desc: event_desc,
    section: section,
    stage: stage,
    group: group,
    mr: "https://gitlab.com/gitlab-org/gitlab/-/merge_requests/#{mr_number}",
    unique: unique_by,
    tiers: tiers
  }).invoke_all
  ['28d', '7d'].each do |days|
    dir_prefix = is_ee ? "ee/" : ""
    event_file_pattern = event_name.delete_prefix('g_project_management_')
    files = Dir["#{dir_prefix}config/metrics/counts_#{days}/*\_#{event_file_pattern}\_*"]
    raise StandardError, "Multiple files found: #{files}" unless files.count == 1
    file_name = files.first

    text = File.read(file_name)
    new_contents = text.gsub(/distribution:/, "events:
  - name: #{event_name}
    unique: #{unique_by}\ndistribution:")

    File.open(file_name, "w") {|file| file.puts new_contents }
  end
end

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

1. Set up snowplow-micro
2. Trigger the events migrated here:
   • create an epic
   • edit an epic's title
   • edit an epic's description
3. Make sure that the events have been triggered with content as per their new event definition files [eg. - category sent as InternalEventTracking] on the http://localhost:9091/micro/good snowplow micro endpoint.

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.