[FEAT]: 🌄 Sunset `Python 3.6`

[adam-grant-hendry]

Description

Python 3.6 reached its end of life on 2021-12-23 (see also PEP 602).

In attempting to update pyproject.toml dependencies, some packages are requiring Python >= 3.7, which may warrant retiring 3.6.

Possible Solution

Please add a DeprecationWarning for Python 3.6 to give existing users time to update their code bases and issue an agreed-upon sunset date for Python 3.6 support.

Additional context

See PR #605 for discussion of some CI workflows that are failing due to outdated dependencies.

Additional context

No response

[Lee-W]

I'm good with this. @woile What do you think? Users using 3.6 can still use version < current version

[woile]

I'm good with this too.