Fix ignored `mypy` errors

[kushagra189]

Currently, for the sake of completing the pipeline, we have ignored certain mypy errors. We need to work on a solution in order to make our code implementation compatible with mypy standards without ignoring these lines.

Suggestion: The majority errors are due to the class-based implementation of foca in order to access it as a property of the Flask Config class. Hence one recommendation is to make the Foca app somehow a parent of the Connexion app, in a similar way that the Connexion app is a parent of the Flask app. Or to extend the Flask app (inside the Connexion) in a way that it has a property foca of type Config.