CompetitionSerializer Simple vs Detail

[bbearce]

@ mention of reviewers

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A brief description of the purpose of the changes contained in this PR.

Codabench is too slow to load. We need to speed up the public competitions page load speed.

Issues this PR resolves

1327

A checklist for hand testing

• [ ] Use automation code from wiki (linked in issue 1327) to create lots of competitions
• [ ] Publish all challenges

  
  docker compose exec django bash
  python manage.py shell_plus
  comps = Competition.objects.all()

for i in comps: i.published = True i.save()

- [ ] See if the page loads any faster

# Checklist
- [ ] Code review by me 
- [ ] Hand tested by me 
- [ ] I'm proud of my work
- [ ] Code review by reviewer
- [ ] Hand tested by reviewer
- [ ] CircleCi tests are passing
- [ ] Ready to merge

[Didayolo]

@bbearce It looks like some tests are missing now (either pytests or e2e) ?

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Trying to fix CircleCI build here:

• 1375

[Didayolo]

Moved the actual change here:

• 1376

@bbearce I let you confirm it is OK