feat(auth): Prefer Private Session support for WebUI Sign In's

[tylerjroach]

• PR title and description conform to Pull Request guidelines.

Issue #, if available:

Description of changes:
This PR allows developers to set a preferPrivateSession flag on web ui sign ins. This launches the CustomTab in an ephemeral state so that the sign in starts from a clean launch. This is especially helpful for social web ui sign-in's where we can't log the end user out of the social account.

How did you test these changes?
(Please add a line here how the changes were tested)

Documentation update required?

• No
• Yes (Please include a PR link for the documentation update)

General Checklist

• Added Unit Tests
• Added Integration Tests
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Ensure commit message has the appropriate scope (e.g fix(storage): message, feat(auth): message, chore(all): message)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

❌ Patch coverage is 53.33333% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 54.25%. Comparing base (3f72bcb) to head (a818581).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3108      +/-   ##
==========================================
- Coverage   54.27%   54.25%   -0.03%     
==========================================
  Files        1038     1038              
  Lines       31991    32009      +18     
  Branches     4700     4703       +3     
==========================================
+ Hits        17363    17365       +2     
- Misses      12788    12804      +16     
  Partials     1840     1840              

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