[CI] pylint upgrade to 2.3.0 and flake8 to latest along with azdev

[haroldrandom]

1. Currently, the pylint azure-cli-extensions is using is 1.9.0, which is behind azdev's pylint==2.3.0. Many features can not enable.
2. Currently, the flake8 azure-cli-extensions is using is 3.5.0. flake8~=3.7.0 starts to recognize feature on Python>=3.5: Support for type hints . Which currently used in src/resource-graph/azext_resourcegraph/custom.py. Enable linter detection on this will have to add another import statement from typing import Any.
   However, typing is added since Python 3.5, so it won't work in Python 2.7. After Python 2.7 retired, we can enable this.

With Python 2 EOF, pylint 2.3.0 and flake8 of latest should be enabled along with azdev's

[yonzhan]

add to S164.