Include generation details in generated client

[emann]

Is your feature request related to a problem? Please describe.
Sometimes when looking at generated clients I notice weird/missing behavior and have no idea what version of openapi-python-client was used to generate it.

Describe the solution you'd like
Pass __version__ and the current time to the init.py template and add a comment to the generated file that looks something like:
# Automatically generated on 6/15/2021 @ 12:00 with openapi-python-client v0.9.2

Describe alternatives you've considered
It may be helpful to have this in every file generated so someone inspecting the source can instantly see it without having to know it exists and go looking for it.