[AADRoleSettings] Fixed issue where missing settings object for a role caused errors.

[ykuijs]

Pull Request (PR) description

This PR fixes an issue where a missing settings object for a role caused errors.

This Pull Request (PR) fixes the following issues

• Fixes Get-MgBetaPolicyRoleManagementPolicyRule : The role setting is not found. #5602

Task list

• Added an entry to the change log under the Unreleased section of the file CHANGELOG.md.
  Entry should say what was changed and how that affects users (if applicable), and
  reference the issue being resolved (if applicable).
• Resource parameter descriptions added/updated in the schema.mof.
• Resource documentation added/updated in README.md.
• Resource settings.json file contains all required permissions.
• Examples appropriately added/updated.
• Unit tests added/updated.
• New/changed code adheres to DSC Community Style Guidelines.