Fix constants in endpoint urls.

[tyte]

Used in lib/utils/repository/challenges/CHALLENGE_TYPE.dart
Using a constant for whole endpoint creates wrong url using dio getItem(). Tested with Api.challengeEventParticipantEndpoint constant.

Constants seem to work with get, but not post.

[Colin-Stark]

There's a database you could use with only one endpoint and it's really easy to maneuver and get your required data

[Colin-Stark]

I could do a sample of your rainbow challenge front app in it for you to see

[karina-klinkeviciute]

@Colin-Stark we already have a backend, it's built with Django. It's a REST API backend. Is the one you're suggesting using GraphQL?

[Colin-Stark]

It's a rest API cloud database using SQL and NoSQL

It's called Harperdb. It is pretty easy to integrate but you already have done that

[karina-klinkeviciute]

@Colin-Stark yes, we have a backend with Django and Python, the code for it is here if you're interested: https://github.com/karina-klinkeviciute/rainbow-challenge/projects/1