Connexion: Introduce typings

[kornicameister]

Description

Long story shorts. I would like to see connexion having typings.
Reason is simple...the codebase is large and quite complicated which makes having a typed code a necessity needed to unveil the functionality behind lines of code.
Obviously speaking we would need to drop support for 2.7 which I voted for in #990 which is not that bad of an idea given that 2.7 is reaching EOL and it's been, I guess, about 10 years since 3.x has been introduced to us.

Expected behaviour

connexion has typed codebase

Actual behaviour

connexion does not have typed codebase

[kornicameister]

@hjacobs what do you say? I can help with making a typings for connexion if you want to.
But let's see if can drop 2.7 first. If so, I will do just that along with creating a plan to proceed with introducing typings.

[rafaelcaricio]

We don't need to drop support for python 2.7 to start introducing typing in the Connexion codebase. https://mypy.readthedocs.io/en/latest/python2.html

[kornicameister]

@rafaelcaricio yeah, it is not needed but 2.7 goes out of the picture in few months. IMHO: No reason to stick around with it.

[hjacobs]

I vote for dropping Python 2.7 support!

[rafaelcaricio]

I vote for dropping 2.7 support as well.

[kornicameister]

@hjacobs @rafaelcaricio

• https://github.com/zalando/connexion/pull/1058
• https://github.com/zalando/connexion/pull/1057