feat: add window config string

[plitzenberger]

Description

This extends the AuthClientLoginOptions interface to include a configuration string used to pass to the window.open function. Using this string allows the user to configure the opened II authentication window.

Tested by locally applying a sample configuration and updating the test suite:

Checklist:

• My changes follow the guidelines in CONTRIBUTING.md.
• The title of this PR complies with Conventional Commits.

Guidance needed 🙏

• I have edited the CHANGELOG accordingly. (should I update the html?)
• I have made corresponding changes to the documentation. (how can I update the docs?)