[Packaging] Support Python 3.9

[jiasli]

Description

Close #16611

It is time to onboard Python 3.9.

Prerequisites

• Bump underlying cryptography-related dependencies to newer versions (Support Python 3.9 #16611)
  • bcrypt 3.2: {Packaging} Bump bcrypt and PyNaCl #17369
  • PyNaCl 1.4: {Packaging} Bump bcrypt and PyNaCl #17369
  • cryptography 3.3.1: {Packaging} Bump cryptography from 2.8 to 3.3.2 #15687
• azdev setup: show error if pip command fails (azdev setup: show error if pip command fails azure-cli-dev-tools#281)
• azdev: support Python 3.9 (Support Python 3.9 azure-cli-dev-tools#280)
• Knack: support Python 3.9 ([CI] Support Python 3.9 microsoft/knack#229)
• Bump Pylint to the latest 2.8.0 ({Pylint} Bump Pylint to 2.8.0 #17861)
• Use azdev and pytest for full test ({CI} Use azdev and pytest for full test #17383)

[yonzhan]

Packaging

[jiasli]

Got error in Check CLI Style task:

https://dev.azure.com/azure-sdk/public/_build/results?buildId=827046&view=logs&j=36dd4138-4d53-5e46-00d9-e5cd9744be05&t=1cf3879c-0a42-5ccd-7693-7a4781d739d8&l=147

src/azure-cli/azure/cli/command_modules/cdn/custom/custom.py:592:29: E1136: Value 'Optional' is unsubscriptable (unsubscriptable-object)

This is caused by pylint-dev/pylint#3882. Need to bump pylint version.