fix(Confluence): method attach_file() to not read() file content

[dunterov]

Resolves #991

Underlying HTTP library supports streaming uploads using file-like objects. So now we just pass infile to attach_content()

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 33.93%. Comparing base (fdaf1ff) to head (0bbaeaa).
⚠️ Report is 23 commits behind head on master.

Files with missing lines	Patch %	Lines
atlassian/confluence.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1535   +/-   ##
=======================================
  Coverage   33.93%   33.93%           
=======================================
  Files          47       47           
  Lines        9091     9090    -1     
  Branches     1232     1232           
=======================================
  Hits         3085     3085           
+ Misses       5884     5883    -1     
  Partials      122      122           

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