Implement user roles and permissions for Admin UI

[niteshpurohit]

Feature Request

Description:

Implement a role-based access control (RBAC) system for the Admin UI, allowing different levels of access (e.g., viewer, editor, admin) for managing materialized views.

Use Case:

In larger teams, it's important to control who can create, edit, or refresh materialized views. For example, a business analyst might have view-only access, while a data engineer has full control.

Proposed Solution:

• Define a set of roles (e.g., :viewer, :editor, :admin).
• Provide a way to map these roles to the host application's current_user (e.g., via a lambda in the initializer).
• Enforce permissions in the UI and API endpoints based on the user's role.

RSpec Tests:

• Configure the authorization callback for different roles.
• (UI) As a 'viewer', visit the dashboard and verify that 'edit' and 'new' buttons are not visible.
• (UI) As an 'editor', verify that CRUD buttons are visible and functional.
• (API) Send a DELETE request as a 'viewer' and verify it is rejected with a 403 Forbidden status.

Checklist:

• I have searched for a similar feature request and didn't find any duplicates.
• I have included all the required information.
• I have tagged the issue with the label "enhancement".

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