text: Title: Remove 3.6 Support
  Body: Python 3.6 has been deemed End of Life (EOL) since December 2021. 
  
  We should make moves to stop supporting it.
  
  # Tasks
  - [ ] Remove 3.6 test support.
  - [ ] Remove 3.6 specific code.
  - [ ] Update `setup.py` to not list 3.6 and set minimum python version to 3.7.
  - [ ] Update any documentation & markdown files to remove reference to 3.6. 
  - [ ] Create pull request with all the changes.
  - [ ] Determine timeline for a merge. With telemetry -- we should be able to confirm whether anyone is using Hamilton with python 3.6. If so then it should be easy to remove, if not, we'll then need to understand what's stopping people from moving to 3.7+. (See @skrawcz to know whether this is the case or not). 
  