fix: optional scopes in refresh token

[monsignore7]

Description

This fix proposes the introduction of a new attribute of the UserManagerSettings class that would be used during the flow of refresh token to decide whether or not to include the scopes as param in the body of the request.
This fix is needed, as I pointed out in #167, because Salesforce doesn't support scope parameter in the body request when refreshing token.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 21.28%. Comparing base (3227179) to head (6761bb3).

Files with missing lines	Patch %	Lines
.../oidc_core/lib/src/managers/user_manager_base.dart	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #169   +/-   ##
=======================================
  Coverage   21.28%   21.28%           
=======================================
  Files          63       63           
  Lines        1809     1809           
=======================================
  Hits          385      385           
  Misses       1424     1424           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.