Add GET Olympians endpoint

As a user,

I should be able to request an index of all Olympians in the system at the endpoint `/api/v1/olympians`

The response should return a 200 status code and be formatted as per the below:

```
{
"olympians":
[
{
"name": "Maha Abdalsalam",
"team": "Egypt",
"age": 18,
"sport": "Diving"
"total_medals_won": 0
},
{
"name": "Ahmad Abughaush",
"team": "Jordan",
"age": 20,
"sport": "Taekwondo"
"total_medals_won": 1
},
{...}
]
}
```