chore: Set redirect_path default in function

[ruhulio]

Description

Set redirect_path default in function instead of as a parameter default in OAuthProxy.

This simplifies how the subclasses need to handle redirect_path and creates a single source of truth for the default as well.

Contributors Checklist

• My change closes #(issue number)
• I have followed the repository's development workflow
• I have tested my changes manually and by adding relevant tests
• I have performed all required documentation updates

Review Checklist

• I have self-reviewed my changes
• My Pull Request is ready for review

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[jlowin]

@ruhulio the windows test failure isn't your fault - it's become flaky in the last day or two.