SNOW-1206259 Handle OKTA Auth invalid responses more gracefully

[sfc-gh-mhofman]

Description

Native OKTA SSO Authn improvements of error handling.

Checklist

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

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 88.88889% with 8 lines in your changes are missing coverage. Please review.

Project coverage is 84.17%. Comparing base (ee843a4) to head (c982f4b). Report is 1 commits behind head on master.

Files	Patch %	Lines
...flake.Data/Core/Authenticator/OktaAuthenticator.cs	88.88%	5 Missing and 3 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #884 +/- ## ========================================== + Coverage 84.11% 84.17% +0.05% ========================================== Files 88 88 Lines 9401 9392 -9 Branches 885 885 ========================================== - Hits 7908 7906 -2 + Misses 1260 1254 -6 + Partials 233 232 -1 ```

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