Blog app: add authorization rules

[Baayeh]

Limiting access to web app resources based on authorization rules.

In this PR, I completed the following tasks:

• Installed CanCanCan in the project.
• Added a role column to the users table.
• Allowed a user to delete a post if it is theirs or if they have an admin role.
• Added the Delete button to the view and made sure that only authorized users can see it.
• Allowed a user to delete a comment if it is theirs or if they have an admin role.
• Added the Delete button to the view and made sure that only authorized users can see it.