Add tracking on `Add seats` button on Duo Pro info card

What does this MR do and why?

Adjust tracking to accommodate both SM and SaaS

Related to https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/8220

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

How to set up and validate locally

1. Enable the following feature flags in the Rails console (bundle exec rails c):

Feature.enable(:code_suggestions)
Feature.enable(:code_suggestions_tokens_api)
Feature.enable(:purchase_code_suggestions)
Feature.enable(:self_managed_code_suggestions)
Feature.enable(:hamilton_seat_management)

1. Setup and start CustomersDot (ideal - but not necessary).
   • if you have CDot running, checkout https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/9089 branch
2. Create or locate a group that is not Free.
3. Visit http://localhost:3000/groups/<GROUP_NAME_ABOVE>/-/usage_quotas#code-suggestions-usage-tab.
4. You should see the Duo Pro tab and "Add seats" button appear.
5. Click "Add seats" button and check the tracking event on Network tab

Attention: the SM part requires !142452 (merged) to be merged. Right now it is just covered with tests