Add FE tracking to subscription management pages
### Problem
Currently we are tracking clicks on subscription card buttons. This shows a general interest on features but doesn't reflect that user wants to actually do this action.
The main goal of this iteration is to be get funnel data (Click on a link on the card -> Click on a purchase confirmation -> Transaction success/fail)
### Proposal
Update the existing tracking for subscription card buttons and add tracking to the actual pages.
Attention: some tracking is already implemented, we would just need to update the event labels & actions.
#### Renew subscription
For all the tracking events set `event_label` as `renew_subscription_sm` / `renew_subscription_saas`
| FE/BE | Page | Description | Event category | Event action |
| ------ | ------ | ------ | ------ | ------ |
|FE| `/subscriptions/` |  <br> User clicks `Renew` button <br> | Webstore | `click_card` |
|FE| `subscriptions/A-S000XXX/renew` |  <br> User clicks `Renew subscription` button <br> | Webstore | `click_renew` |
|BE| - | Transaction is successful | SubscriptionsController | `transaction_successful` |
|BE| - | Transaction has failed | SubscriptionsController | `transaction_failed` |
#### Add seats
For all the tracking events set `event_label` as `add_seats_sm` / `add_seats_saas`
| FE/BE | Page | Description | Event category | Event action |
| ------ | ------ | ------ | ------ | ------ |
|FE| `/subscriptions/` |  <br> User clicks `Add seats` button <br> | Webstore | `click_card` |
|FE| `/subscriptions/A-S000XXX/edit?transaction=extra_seats` |  <br> User clicks `Purchase seats` button <br> | Webstore | `click_purchase` |
|BE| - | Transaction is successful | SubscriptionsController | `transaction_successful` |
|BE| - | Transaction has failed | SubscriptionsController | `transaction_failed` |
#### Upgrade subscription
For all the tracking events set `event_label` as `upgrade_subscription_sm` / `upgrade_subscription_saas`
| FE/BE | Page | Description | Event category | Event action |
| ------ | ------ | ------ | ------ | ------ |
|FE| `/subscriptions/` |  <br> User clicks `Upgrade plan` button <br> | Webstore | `click_card` |
|FE| `subscriptions/A-S000XXX/upgrade/new` |  <br> User clicks `Upgrade subscription` button <br> | Webstore | `click_upgrade` |
|BE| - | Transaction is successful | SubscriptionUpgradesController | `transaction_successful` |
|BE| - | Transaction has failed | SubscriptionUpgradesController | `transaction_failed` |
#### Change linked namespace
For all the tracking events set `event_label` as `change_namespace` (as this is only possible for SaaS)
| FE/BE | Page | Description | Event category | Event action |
| ------ | ------ | ------ | ------ | ------ |
|FE| `/subscriptions/` |  <br> User clicks `Change linked namespace` button <br> | Webstore | `click_card` |
|FE| `subscriptions/A-S000XXX/edit?transaction=change_gitlab_group` |  <br> User clicks `Confirm changes` button <br> | Webstore | `click_change` |
|BE| - | Transaction is successful | SubscriptionsController | `transaction_successful` |
|BE| - | Transaction has failed | SubscriptionsController | `transaction_failed` |
#### Cancel subscription
For all the tracking events set `event_label` as `cancel_subscription_sm` / `cancel_subscription_saas`
**Attention:** The modal only exists for SaaS users
| FE/BE | Page | Description | Event category | Event action |
| ------ | ------ | ------ | ------ | ------ |
|FE| `/subscriptions/` |  <br> User clicks `Cancel subscription` button <br> | Webstore | `click_card` |
|FE| `subscriptions/` |  <br> In the modal that appears user clicks `Cancel subscription` button <br> | Webstore | `click_modal` |
|BE| - | Transaction is successful | SubscriptionsController | `transaction_successful` |
|BE| - | Transaction has failed **Note:** we don't have a try/catch around this action, we might need to add it to catch this failure | SubscriptionsController | `transaction_failed` |
#### Resume subscription
For all the tracking events set `event_label` as `resume_subscription_sm` / `resume_subscription_saas`
**Attention:** There is extra confirmation, the click on the button on the card is the only FE event
| FE/BE | Page | Description | Event category | Event action |
| ------ | ------ | ------ | ------ | ------ |
|FE| `/subscriptions/` |  <br> User clicks `Resume subscription` button <br> | Webstore | `click_card` |
|BE| - | Transaction is successful | SubscriptionsController | `transaction_successful` |
|BE| - | Transaction has failed | SubscriptionsController | `transaction_failed` |
### Result
### Next steps (if any)
- [x] Update dashboard: https://gitlab.com/gitlab-data/product-analytics/-/issues/1063+
### How will we measure success?
epic