Implement type annotations

[holtgrewe]

Problem

Python type annotations are very useful as they enable many static checks and eliminate whole classes of bugs. Plus, you get really nice type-safe editor autocompletion. There are type annotations available for Django. sodar-core based sites cannot fully benefit from this as django-sodar-core package is missing type annotations.

Solution

Implement type annotations and add static type checking as a CI check.

Alternative Solutions

• keep as is
• provide a sodar-core-types package

Additional Context

I would recommend pyright over mypy as the type checking engine.

[holtgrewe]

CC @tedil who is an expert in Python type annotations

[mikkonie]

Dupe of #568, closing.