Create new delivery target - Coder Inbox

[defelmnq]

Part of the main PR visible here.

This PR scope is to create the new delivery target internally for Coder Inbox. It includes :

• The DB Migration
• The logic to insert notifications to Coder Inbox

DB Migration discussed :

CREATE TABLE notifications_inbox (
    id UUID PRIMARY KEY,
    user_id UUID, // Foreign key to users
    title TEXT,
    content TEXT,
    read_at TIMESTAMP, // using NULL to know that the notification has not been read
    created_at TIMESTAMP NOT NULL DEFAULT NOW()
);

This PR also includes RBAC policy.