fix: remove user registration emails

[amandazhuyilan]

Description

Remove sending emails to new users who has registered for a BioCommons account, and update sending emails to bundle admins upon new request.

Changes

• Removed the admin notification helper so the BioCommons router no longer knows how to compose or enqueue the “New BioCommons User Registration” email
• Update bundle requests to trigger admin emails. When someone registers for a bundle whose group membership isn’t auto‑approved (like TSI), the registration handler now looks up the group admins, composes the approval notice, and enqueues an email for each admin before committing the transaction.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have added unit / integration tests that prove my fix is effective or that my feature works
• I have run all tests locally and they pass
• I have updated the documentation (if applicable)
• For any new secrets, I have updated the shared spreadsheet and the GitHub Secrets.

[marius-mather]

It'd be nice to simplify this code a bit if possible - I know we can put in guards against every possible missing value, but it bloats out our code. Let's do some basic checks, but otherwise deal with issues when they actually arise

[marius-mather]

looks good, thanks!