python2 removal

[gonchik]

Hi!

time to skip python 2.x versions. Yes, I waited 5 years until last super old servers will be updated, and last a few months were upgraded.
I am happy to skip python2 support.

Steps:

Remove Github actions
Remove string formats make for pythonic 3.
Update pypi
Adjust linter, black
Review tests
3.41.x will be latest supported version with python2
next release will start from 4.0.0 fully support 3.9 and newer based on the https://devguide.python.org/versions/
use more and more python3 sugar codes.
Welcome to contribute.

Cheers,
Gonchik Tsymzhitov

#1514

[codecov]

Codecov Report

Attention: Patch coverage is 6.48012% with 635 lines in your changes missing coverage. Please review.

Project coverage is 34.06%. Comparing base (c2f3382) to head (75506cc).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
atlassian/jira.py	4.68%	183 Missing ⚠️
atlassian/statuspage.py	0.00%	96 Missing ⚠️
atlassian/bitbucket/__init__.py	7.79%	71 Missing ⚠️
atlassian/bamboo.py	1.40%	70 Missing ⚠️
atlassian/confluence.py	0.00%	69 Missing ⚠️
atlassian/xray.py	0.00%	46 Missing ⚠️
atlassian/service_desk.py	32.35%	23 Missing ⚠️
atlassian/insight.py	0.00%	16 Missing ⚠️
atlassian/portfolio.py	0.00%	12 Missing ⚠️
atlassian/crowd.py	0.00%	9 Missing ⚠️
... and 16 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1515      +/-   ##
==========================================
- Coverage   34.06%   34.06%   -0.01%     
==========================================
  Files          46       46              
  Lines        8832     8833       +1     
  Branches     1352     1194     -158     
==========================================
  Hits         3009     3009              
- Misses       5698     5702       +4     
+ Partials      125      122       -3     

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