Updated code structure

Folder structure updates:

1. Introduced api folder at the root of project that handles various functions in the network layer like:
   1. Parsing requests
   2. Authorization
   3. Rendering responses etc..
2. Since we are moving ahead with gin all the APIs defined in the service interface will have the structure:
   FunctionName(ctx *gin.Context)
3. Added usecase folder inside internal that houses all the functionalities defined as per business requirements. Our APIs depends on these functionalities directly.
4. Added deps folder that contains all the dependencies of our usecase as different interfaces. These interfaces are implemented by their corresponding components.

As an example, a vehicle service is created that exposes 3 APIs:

1. Create Vehicle
2. Get Vehicle
3. List Vehicles

The above 3 APIs are 3 different business requirements and needs to be defined in the usecase interface. To implement this, the usecase depends on vehicles component. This component implements the VehicleRepo dependency inside it's internal package and exposes the functions through vehicle.MakeRepo().