[SM Cloud Licensing Trials] TrialAccount and BillingAccount

The following discussion from !12050 should be addressed:

• @vitallium started a discussion: (+11 comments)

  I think this will create a lot of confusion and cognitive burden because, instead of having one way to check an account, we will need to check two. My question is: can't we reuse the BillingAccount for trials? If necessary, we could mark a billing account as a trial. Trial accounts should behave the same as regular billing accounts, except that they would use different plans.

In !12050 we are introducing a TrialAccount which exists alongside the BillingAccount

This creates two places to check for an account.

Questions

1. Should we use BillingAccount for trials?
2. Should we convert BillingAccount into a generic Account object to be reused?
3. Should we create an Account abstraction that holds BillingAccount and TrialAccount ?