[Endpoints] Scheduling appointment endpoints

[LucaStefan112]

Create the endpoints for the appointment component. The component will need this main endpoints:

• Get hospital specialisations
• Get doctors for a certain specialization
• Get available scheduling intervals for a certain doctor in a certain time-frame
• Schedule appointment for a user, in a certain interval with a certain doctor

Future endpoints will be added

[omerdikyol]

@MariusAchitei you might need to add "specialization" attribute to the user to get doctors for a certaion specialization: specialization: string; and specialization: { type: String, required: false, enum: <You can create array at ./src/helper/enum.ts, then import it and write it here>, },