[Packaging] Bump embedded Python to 3.8 for deb packages

[jiasli]

Context

Python 3.6 has reached its End of Life on 2021-12-23 (https://www.python.org/downloads/) and there will be no security updates, which puts Azure CLI deb packages at risk.

Change

This PR bumps Python to 3.8.11 for deb packages.

Question: Should we use Python 3.9 or even Python 3.10? Windows MSI currently contains Python 3.8.9.

Related PRs

• Drop Python 3.6 support #19858
• {Packaging} Upgrade python version to 3.6.10 in deb package #13565

History Notes

[Packaging] Bump embedded Python to 3.8 for deb packages
[Packaging] BREAKING CHANGE: Drop support for Ubuntu 14.04 Trusty Tahr and Debian 8 Jessie

[jiasli]

CI fails on jobs:

• Build Deb Packages Trusty (Ubuntu 14.04)
• Build Deb Packages Jessie (Debian 8)

https://dev.azure.com/azure-sdk/public/_build/results?buildId=1267742&view=logs&j=1c081627-a4dd-57ff-b320-9981b0ff7f6f&t=fab9ebe1-3cad-5c96-61ed-c5bfa2e064ad&l=9616

2021-12-29T08:25:58.3150877Z Could not build the ssl module!
2021-12-29T08:25:58.3151326Z Python requires an OpenSSL 1.0.2 or 1.1 compatible libssl with X509_VERIFY_PARAM_set1_host().
2021-12-29T08:25:58.3152432Z LibreSSL 2.6.4 and earlier do not provide the necessary APIs, https://github.com/libressl-portable/portable/issues/381

This is because LibreSSL on These distributions are too old. It turns out that building Python 3.7+ on old distributions like these is complex, as we need to manually build openSSL as well:

• https://jameskiefer.com/posts/installing-python-3.7-on-debian-8/
• https://bugs.python.org/issue34028
• https://stackoverflow.com/questions/53543477/building-python-3-7-1-ssl-module-failed

Per https://wiki.ubuntu.com/Releases, Ubuntu 14.04.6 Trusty has reached its End of Standard Support in April 2019.
Per https://wiki.debian.org/DebianReleases, Debian 8 Jessie has reached its EOL LTS on 2020-06-30.

Perhaps it is time to drop support for Ubuntu 14.04.6 Trusty and Debian 8 Jessie as well.