refactor: do batched requests for braze tracking in lic assignment

[iloveagent57]

Description

Currently, each call to track license lifecycle state (e.g. during license assignment) seems to make 2 calls to braze per license:

1. Call to create_braze_alias.
2. Call to track_user.

This is an attempt to utilize the braze API more efficiently. If we don’t, we’re going to end up making around 1 million calls to braze during the execution of a script that assigns 400,000 emails. The risk here is that we get rate-limited, or just see "normal" failed requests to braze, and many users/licenses end up in a partially tracked state that leads to difficulties/support-overhead during license activation.

Another subtle change here: as part of assignment, we conditionally want to send assignment notification emails. These require that we have braze aliases setup. I've re-ordered the chain of tasks we kick off to only explicitly create braze aliases in a task IF we're going to send those notifications.
Note that the task to track license changes also creates braze aliases during assignment (so we can track users who don't have an lms_user_id yet). It's fine to do the alias tracking call multiple times (its idempotent on the Braze side), especially now that we're doing all alias creation as batched work. But with this second change, we now will only create aliases at one point (during lifecycle tracking) when assignment notification is disabled.

Link to the associated ticket: https://openedx.atlassian.net/browse/ENT-8304

Testing considerations

• Ran a manual test in the braze dev account, results captured in ticket.

Post-review

Squash commits into discrete sets of changes

[pwnage101]

The rest LGTM, just curious about not sending segment events anymore!