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

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 ](https://docs.python.org/zh-cn/3/library/typing.html). 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