[SM Cloud Licensing Trials] Add TrialAccount Association to License Model
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### Problem
Follow-up from https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/12078#note_2381042663
In https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/12295+, we introduced the ability to create a license record from a `Trial` and its associated `TrialAccount` for SM online cloud licensing trials.
However, the `License` model currently does not have a direct association to a `TrialAccount`, and because trials are not stored in Zuora, there would also be no associated `BillingAccount`
[Similar to how we save legacy trial licenses today](https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/6ff3e502e30a42c4e9247fa0d8240b6856ca872f/app/services/marketo/create_license_service.rb#L54), the `License` record instead saves attributes like `company`, `name` and `email` to the license directly. In the case of online cloud licensing trials, this is just duplicated data from a `TrialAccount`.
This could lead to potential problems in the future such as
1. Needing to use inefficient and indirect queries to find licenses owned by a specific `TrialAccount`
- Ex: Matching `name`, `company` and `email` to the `TrialAccount`, or going through the license's associated `CloudActivation`, etc.
3. Possible data discrepancies between a `TrialAccount` and the account data saved to the `License` directly
- Ex: If we allow a user to manage or update their trial account in the future, the license also needs to be updated separately
4. More overhead and complexity in trying to understand our data model
### Proposal
**Important:** The proposal here could change depending on the outcome of https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/12394+
- Add an optional association to a `TrialAccount` in the `License` model
- Update the `build_from_trial` method in the `License` model to also save a `trial_account_id` in its attributes
issue