Support custom HTTP proxy setting: QDT_PROXY_HTTP

[Guts]

No description provided.

[codecov-commenter]

Codecov Report

Merging #293 (e96fc06) into main (fd1e353) will increase coverage by 1.43%.
The diff coverage is 73.52%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #293      +/-   ##
==========================================
+ Coverage   63.42%   64.85%   +1.43%     
==========================================
  Files          36       36              
  Lines        2075     2097      +22     
  Branches      440      450      +10     
==========================================
+ Hits         1316     1360      +44     
+ Misses        648      615      -33     
- Partials      111      122      +11     

Impacted Files	Coverage Δ
qgis_deployment_toolbelt/utils/journalizer.py	71.42% <33.33%> (+0.51%)	⬆️
qgis_deployment_toolbelt/cli.py	78.84% <55.55%> (-5.94%)	⬇️
qgis_deployment_toolbelt/utils/proxies.py	80.00% <82.35%> (ø)
qgis_deployment_toolbelt/utils/file_downloader.py	82.50% <100.00%> (ø)

... and 1 file with indirect coverage changes