[Atlassian] Issue of not using proxies inside rest client session

[flok]

Adds the provided proxies to the request session after creation.
Without this the proxies will not be used to download attachements for example.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 34.07%. Comparing base (9eb04fd) to head (fa5d81c).
Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
atlassian/rest_client.py	0.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1488      +/-   ##
==========================================
- Coverage   34.10%   34.07%   -0.04%     
==========================================
  Files          46       46              
  Lines        8753     8755       +2     
  Branches     1335     1232     -103     
==========================================
- Hits         2985     2983       -2     
- Misses       5646     5650       +4     
  Partials      122      122              

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