BE-Generate heats

[MarisiaS]

This PR address issue #57

Implementation

1. backend/api/serializers/GenerateHeatSerializer.py

Added two serializers:

• AthleteSeedSerializer: Contains two fields, athlete of type PrimaryKeyRelatedField and seed_time of type HeatDurationField.
• GenerateHeatSerializer: Introduces a unique field athletes of type AthleteSeedSerializer, expecting multiple records. This serializer has two functions: create: Accepts a list of athletes, sorts them by seed time, and generates corresponding heats. calculate_lane_num: An auxiliary function to calculate the lane number of an athlete.

2. backend/api/views/GenerateHeatView.py This view utilizes GenerateHeatSerializer and comprises three functions:

• get_queryset: Accepts a group_id and filters all athletes corresponding to that group.
• post: Receives an event_id along with a list of athletes and their seed times, then creates heats corresponding to that event.
• delete: Given an event_id, removes all heats related to that event.

3. backend/api/urls.py

Introduced the event_heat// endpoint that utilizes GenerateHeatView.

[MarisiaS]

Just a general suggestion regarding the code style would be adding spaces between operators. @viriponce I added the spaces!