[Tour of Beam] [Task] Create OpenAPi spec for ToB backend and frontend

[olehborysevych]

What needs to be done:

Consider creating OpenAPI spec for Tour of Beam backend functions.
Consider using the spec to deploy Cloud endpoint or API Gateway
Automate deployment of managed API service using the spec.
Consider using the spec to generate flutter clients and use them on the front side

Priority:

P3

Components:

tour-of-beam