@ mention of reviewers`

@Didayolo`

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

This is a first PR in the optimization effort to load codabench quickly. The following are done in this PR:

Adde new fields to competition modal participants_count and submissions_count
Used these fields in the competition detail page
Used participants_count field in public competitions page
Used participants_count field in the popular competitions section in home page

On the backend, serializers are changed to use this new filed instead of the annotated values from the queries.

when you upload a new submission, submissions_count will be updated (+1)
When you delete a submission, submissions_count will be updated (-1)
When a new participant joins the competition (even not approved yet) the participants_count will update (+1)
participants_count is never decremented because we do not delete a participant we only revoke the status

1. Migration

docker compose exec django ./manage.py migrate

2. Update counts for all competitions

Bash into django console

docker compose exec django ./manage.py shell_plus

Import and call the function

from competitions.submission_participant_counts import compute_submissions_participants_counts
compute_submissions_participants_counts()