[Feature Flag modification] Override the userID within the unleash context to send billing account ID instead

Problem

As part of [Feature flag] Enable multiple billing account ... (#11222), we want to enable the feature flag for certain billing account IDs instead of userIDs.

Proposal

A possible solution here is to override the unleash_context's user_id within unleash_helper and pass the billing_account ID instead.

Result

Next steps (if any)

How will we measure success?