feat: update billing manager sync to use a single func

[zlwaterfield]

Changes

Follow up to https://github.com/PostHog/billing/pull/797 and https://github.com/PostHog/billing/pull/817.

We want to sync more useful user data into billing to trigger the emails/events. We don't have the proper email/distinct id/role information right now.

This PR does two things:

• pulls together billing syncs into a single function - right now multiple calls are made and it's inefficient. Doesn't change any existing sync data because billing still relies on them. They can be removed in the future once it no longer does.
• adds a new key org_admin_user to the sync with dinstinct_id, email and role. This is only for admins and owners because billing-related notifications are needed only for admins and owners.

Given this is only syncing admins and owners it's not adding to much extra data.

The hope with this is we will be able to trigger events in billing that can then use the CDP to trigger emails whether than be in c.io or the CDP directly.

👉 Stay up-to-date with PostHog coding conventions for a smoother review.

Does this work well for both Cloud and self-hosted?

It doesn't have an impact

How did you test this code?

Updated tests

[sentry-io]

Suspect Issues

This pull request was deployed and Sentry observed the following issues:

• ‼️ AttributeError: 'NoneType' object has no attribute 'update_billing_organization_users' posthog.management.commands.sync_to_billing in ... View Issue
• ‼️ Exception: ('Billing service returned bad status code: 400', 'body:', {'type': 'validation_error', 'code': '... posthog.tasks.sync_to_billing.sync_to_billing View Issue

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