- Track tax link in order summary

- Track render of SaaS Checkout page

- Add the body data to the checkout layout so it has the proper
  context (category) when triggering the tracking in snowplow.

- Track render of Billing page

- Track clicks on edit steps in checkout

- Fix naming of snakeCasedStep since what was called snakeCasedStep was
  actually dash-case/kebab-case.

- Track subscriptionsDetails events on form transition

- Track billingDetails events on form transition

- Track paymentMethod events on form transition

- Track Confirm Purchase

- Zuora iframe will likely not respond with
  error messages unless something goes very wrong.
  Since all card related errors are processed
  within it's iframe until resolved.

- Refactor Step constants for subscriptions

- Step has been changed to only have to know to emit events the steps
  are responsible for the tracking, this also makes it so Step
  doesn't have to pull in the getters & state to be able to
  pass the data on to the tracking.

- refs:
  https://gitlab.com/gitlab-org/gitlab/-/issues/342853
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_802788391
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_804004486
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_804004490
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_804004492
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_804555436
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_804555439
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_804555440
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_804555442
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_804555444
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_784574426
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_810556340
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_817671640
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_817671638
  https://gitlab.com/gitlab-org/gitlab/-/merge_requests/74828#note_817671634

- Lessons some of the concerns expressed in:
  https://gitlab.com/gitlab-org/gitlab/-/issues/350344