Upgrade Python to v3

[lin-d-hop]

Description

Looks like it's time to upgrade from Python 2.7 to 3 🙈

Collecting ruamel.ordereddict; platform_python_implementation == "CPython" and python_version <= "2.7"
  Downloading ruamel.ordereddict-0.4.15-cp27-cp27mu-manylinux1_x86_64.whl (93 kB)
Collecting ruamel.yaml.clib>=0.1.2; platform_python_implementation == "CPython" and python_version < "3.10"
  Downloading ruamel.yaml.clib-0.2.4.tar.gz (180 kB)
    ERROR: Command errored out with exit status 1:
     command: /opt/hostedtoolcache/Python/2.7.18/x64/bin/python -c 'import sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-8d1HNj/ruamel-yaml-clib/setup.py'"'"'; __file__='"'"'/tmp/pip-install-8d1HNj/ruamel-yaml-clib/setup.py'"'"';f=getattr(tokenize, '"'"'open'"'"', open)(__file__);code=f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-pip-egg-info-Mgwt0S
         cwd: /tmp/pip-install-8d1HNj/ruamel-yaml-clib/
    Complete output (1 lines):
    minimum python version(s): [(3, 5)]
    ----------------------------------------
ERROR: Command errored out with exit status 1: python setup.py egg_info Check the logs for full command output.

Acceptance Criteria & Tests

1. OFN is on Python 3