GET `/api/regions/active`

**Description**

Some regions in the enrollment flows are not active or valid and should not appear in any selector. We need a new endpoint to return only active regions.

~~**Possible strategy**~~

~~1) Retrieve all `TeamSeasons`~~
~~2) Filter `TeamSeasons` based on their start date (to determine whether they are active or not)~~
~~3) Get `regions` through the following relation `Team_Season__r.Team__r.School_Site__r.Region__c`~~

**Endpoint**: `GET /api/regions/active`

**Response**:
```json

{
["Region 1", "Region 2", "Region 3"]
}

```
~~