Send email campaign usage data

What does this MR do?

Issue: https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/308

With !53715 (merged) we will rollout in-product-marketing emails to self managed and want to gather usage data (sent emails and cta-clicks).

Queries

Gitlab::UsageData.count(Users::InProductMarketingEmail.group(:track, :series)) (Postgres.ai)

Queries

SELECT COUNT("in_product_marketing_emails"."id") AS count_id,
       "in_product_marketing_emails"."track" AS in_product_marketing_emails_track,
       "in_product_marketing_emails"."series" AS in_product_marketing_emails_series
FROM "in_product_marketing_emails"
GROUP BY "in_product_marketing_emails"."track",
         "in_product_marketing_emails"."series"

Plan

 Aggregate  (cost=0.29..2309.69 rows=12 width=12) (actual time=5.991..26.871 rows=12 loops=1)
   Group Key: in_product_marketing_emails.track, in_product_marketing_emails.series
   Buffers: shared hit=3759
   ->  Index Scan using index_in_product_marketing_emails_on_user_track_series_cta_clic on public.in_product_marketing_emails  (cost=0.29..1921.43 rows=51752 width=12) (actual time=0.034..14.569 rows=51752 loops=1)
         Buffers: shared hit=3759

Gitlab::UsageData.count(Users::InProductMarketingEmail.where.not(cta_clicked_at: nil).group(:track, :series)) (Postgres.ai)

SELECT COUNT("in_product_marketing_emails"."id") AS count_id,
       "in_product_marketing_emails"."track" AS in_product_marketing_emails_track,
       "in_product_marketing_emails"."series" AS in_product_marketing_emails_series
FROM "in_product_marketing_emails"
WHERE "in_product_marketing_emails"."cta_clicked_at" IS NOT NULL
GROUP BY "in_product_marketing_emails"."track",
         "in_product_marketing_emails"."series";

 Aggregate  (cost=0.29..691.21 rows=1 width=12) (actual time=1.200..1.200 rows=0 loops=1)
   Group Key: in_product_marketing_emails.track, in_product_marketing_emails.series
   Buffers: shared hit=200
   ->  Index Scan using index_in_product_marketing_emails_on_user_track_series_cta_clic on public.in_product_marketing_emails  (cost=0.29..691.19 rows=1 width=12) (actual time=1.198..1.199 rows=0 loops=1)
         Index Cond: (in_product_marketing_emails.cta_clicked_at IS NOT NULL)
         Buffers: shared hit=200

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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