feat(proxies): use pypac to use PAC file

[jmkerloch]

Introduce support for PAC file for proxy definition.

QDT will first try to use QDT_PROXY_HTTP environment variable then new environment variable QDT_PAC_FILE for custom PAC file then system PAC if available.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 82.75862% with 5 lines in your changes missing coverage. Please review.

Project coverage is 70.86%. Comparing base (81e2b4d) to head (a866e54).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
qgis_deployment_toolbelt/utils/proxies.py	82.14%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #560      +/-   ##
==========================================
- Coverage   71.00%   70.86%   -0.14%     
==========================================
  Files          47       47              
  Lines        3135     3158      +23     
  Branches      671      680       +9     
==========================================
+ Hits         2226     2238      +12     
- Misses        718      728      +10     
- Partials      191      192       +1     

Flag	Coverage Δ
unittests	70.29% <82.75%> (-0.14%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
qgis_deployment_toolbelt/commands/upgrade.py	62.63% <ø> (ø)
...eployment_toolbelt/profiles/remote_http_handler.py	36.53% <ø> (ø)
qgis_deployment_toolbelt/utils/file_downloader.py	77.04% <100.00%> (ø)
qgis_deployment_toolbelt/utils/proxies.py	66.66% <82.14%> (-10.76%)	⬇️

[sonarcloud]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud