Make it work with Python 3.7

[lcian]

The Python SDK supports Python 3.6, so we need to make the package work with it if we wanna use it there.
A solution is to define the TypedDict only if the Python version is >= 3.8, the SDK won't use it anyways.

[linear]

CON-63 Make it work with Python 3.6

[cleptric]

The upcoming python SDK major only supports 3.7 afaik.