[SNOW-1881731] Add externalBrowser, oauth, okta, keypair automated authentication tests

[sfc-gh-pcyrek]

Description

Please explain the changes you made here.

This PR adds automated tests for externalBrowser, oauth, okta, keypair authentication methods

Checklist

• Code compiles correctly
• Code is formatted according to Coding Conventions
• Created tests which fail without the change (if possible)
• All tests passing (dotnet test)
• Extended the README / documentation, if necessary
• Provide JIRA issue id (if possible) or GitHub issue id in PR name

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.33%. Comparing base (444a2c1) to head (b75825e).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1082      +/-   ##
==========================================
+ Coverage   86.23%   86.33%   +0.10%     
==========================================
  Files         132      132              
  Lines       12664    12664              
  Branches     1299     1299              
==========================================
+ Hits        10921    10934      +13     
+ Misses       1417     1406      -11     
+ Partials      326      324       -2     

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