Add events index endpoint

As a user,

I can see a list of all events, broken down by sport type by submitting a get request to the endpoint `/api/v1/events`.

The response should be formatted as follows:
```JSON
{
"events":
[
{
"sport": "Archery",
"events": [
"Archery Men's Individual",
"Archery Men's Team",
"Archery Women's Individual",
"Archery Women's Team"
]
},
{
"sport": "Badminton",
"events": [
"Badminton Men's Doubles",
"Badminton Men's Singles",
"Badminton Women's Doubles",
"Badminton Women's Singles",
"Badminton Mixed Doubles"
]
},
{...}
]
}
```