[PLTFRM-1510] Set highlight-mfa-users to Admin and Editor roles by default

[kat3samsin]

Description

Pre-review checklist

Please make sure the items below have been covered before requesting a review:

• This change works and has been tested locally or in Codespaces (or has an appropriate fallback).
• This change has relevant unit tests (if applicable).
• This change has relevant documentation additions / updates (if applicable).
• I've created a changelog description that aligns with the provided examples.

Pre-deploy checklist

• VIP staff: Ensure any alerts added/updated conform to internal standards (see internal documentation).

Steps to Test

1. vip dev-env create && vip dev-env start
2. Navigate to WP Admin > Users page
3. Verify the notice for 2FA shows Admin and Editor instead of high privileges

[Copilot]

Pull Request Overview

This PR modifies the highlight-mfa-users module to default to Admin and Editor roles instead of using configurable capabilities. The change simplifies the configuration by hard-coding the roles to DEFAULT_ADMIN_EDITOR_ROLE_SLUGS and forces the notice display to show "Administrator and Editor" rather than "high privileges".

• Hard-codes the MFA highlighting to apply only to Admin and Editor roles
• Removes the capability-based configuration in favor of role-based defaults
• Forces the notice to display specific role names instead of generic "high privileges" text

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[pandah3]