feat: API to list role-holder addresses

[jennifer-richards]

Adds API endpoint needed to decouple the makewhitelist script from the datatracker.

The code is refactored compared to the old list-role-holder-emails script (final version here), but I confirmed that at least for a recent dev database, the refactored and original code agree.

Also: I've reused the ietf.api.views.email_aliases API token here because it's what the rest of the API calls used by the postconfirm scripts use. I'm a little uneasy about the now misleading name, but have kept it for operational simplicity. I'd be open to either renaming the token or using a dedicated token for this endpoint.

[rjsparks]

I think we should use a separate api token named for this view. We may have additional clients of the APIs in the future, and we should be able to make the decision to limit one of the other of these endpoints from those additional clients.

[rjsparks]

The functionality looks fine. The list of groups to scrape from should get leadership review (I expect we will add groups and group types to it), but that does not have to happen now.

[jennifer-richards]

I think I'm done now. In addition to straightening out the API token reuse, I realized I'd deviated from the pattern used for the last few API endpoints. I've refactored to do the Group-specific work in ietf.group.utils.role_holder_emails() and put the API-specific interface in ietf.api.views.role_holder_addresses().

May not be perfect, but it's at least consistent.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.83%. Comparing base (187c2c5) to head (d2f81a3).
Report is 92 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7291      +/-   ##
==========================================
- Coverage   88.98%   88.83%   -0.15%     
==========================================
  Files         291      291              
  Lines       40717    40881     +164     
==========================================
+ Hits        36233    36318      +85     
- Misses       4484     4563      +79     

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